Electric Flux Density, D, is a conceptual/graphical vector field that we use to get a “feel” for a complicated electric field made by source charges; it ignores alternations made to the electric field caused by the presence of material objects. What is exactly an electric flux, as you ask, is called a flux line. A flux line represents the trajectory a positive test charge would take if placed at that point, or the force a positive test charge would experience if placed at that point.1 Flux lines aren’t real, they’re just useful for visualization, and the number of them that emanate from a charge is arbitrarily set; in SI units, 1 flux line will emanate from 1 C.2

I would also like to point out that the answer given by André Michaud is verbatim the definition of electric current, and must be a misunderstanding of your question.

1. From Introduction to Electrodynamics by Griffiths

2. From Elements of Electromagnetics by Sadiku

Have you ever listen to Professor Walter Lewin?

Here is the Lecture of the Professor on Electric Flux. Let me know if this helps.  

https://www.youtube.com/watch?v=vxasQBBlWmk&ab_channel=FortheAllureofPhysics

In simple terms, the electric flux density is a measure of the number of electrons that flow through a given surface in an electrical wire.

The magnetic flux is also a measure of the magnetic intensity resulting from the passage of electrons across a given surface.

Moving electrons are the particles that mediate both electric and magnetic properties in electric wires.

If you can get hold of an old undergrad "Physics" by Halliday and Resnick, or "University Physics" by Sears Zemansky and Young, all aspects of electric and magnetic behavior are simply explained.

Electric flux density is proportional to Electric field strength, but in dielectrics it is corrected to take out the effect of surface and volume polarization charges, and the Electric field is not corrected so is lower.   The lines of electric flux do not exist, but they are the lines that show the direction of the electric force on an infinitesimal charge at that point.  They are drawn close together to represent stronger force.  The way the laws of electromagnetics are means that the lines can consistently be drawn like this.  By that I mean that if the forces in two places point a bit towards each other, then the lines get closer together in that direction, and the forces do actually get stronger too.

The forces are actually proportional to the electric field (E), not to the electric flux density (D).

They are line lines drawn from a mountain peak showing the way that something would start to slide down.  The lines don't exist, but the force is real.

Since this question is a basic question i would like to give an answer to it in spite of being late.

In the electrostatic each charge Q has an electric field which is its domain of influence on other electric charges. The electric field has an intensity which is the force acting on a positive point charge located in the point of interest at a distance r from the point charge Q. So if a charge q is at the position r in the field region of Q, it will suffer from a force F= qE, with E is the electric field and q is the charge. As a force both F and E are vectors.

This description is a direct consequence of the Coulomb law.

In order to take the effect of the the electric field on a medium into consideration, one has to define the a quantity termed the electric flux density D. It is found that D is proportional is proportional to E with proportionality constant is called the permitivity of the medium epsilon.

So D= epsilon E. For the vacuum, epsilon is equal to epsilon0 which is the permitivity of free space. The epsilon could be measured in units of epsilon0 such that epsilon= dielectric constant epsilon0,

In order to understand the meaning of E and D can be best achieved when we return to the parallel plate capacitor.

Assume that we have a parallel plate capacitor with area A and separation d. Assume further that there is vacuum in the capacitor,

By applying ac DC voltage V on the capacitor, an electric field E will be formed in the space between the plates which is given by the voltage gradient E= V/d,

The capacitor will be charged by charge Q= CV, C =epsilon0 A/d,

Then Q=epsilon0 A V/d,

And Q/A= epsilon0 E.==D, Therefore, D which is the electric displacement,

or the electric flux density is equal to the charge density on the surface of the charged capacitor.

This relation can be derived directly from the Gauss relating the electric charges by the electric flux where the electric flux originating from charge Q= this charge. Enclosing this charge by a sphere, one gets what is called the electric flux density D on this surface.

Then integral on a closed surface of D.dS= the electric flux epsi= Q

Enclosing the one centimeter square of the inner surface of the capacitor plate by a closed surface one D= epsilon0E

Best wishes

the flux of electrical field is defined numerically as the amount of charge located at certain position or area . these charges affects the space around it and alter its electrical characteristics , this area being electrically modified by the charge is known as the field of the charge , any other charge that may be located in the field area will interact electrically with the field-originating charge , this interaction generates a force that may lead to attraction or repulsion of the charges

this phenomenon is described mathematically by coulombs law .

in vector analysis this force is a vector field that has both direction and magnitude , thus people that the electrical field is (vectors or lines)

but in fact the vector is completely differnt from a line

as it is no thing more than a mathematical representation to two quantites

the magnitude and the direction ,please look at this link

https://en.wikipedia.org/wiki/Vector_field

thus we can say that the force effect is so real but the lines / vectors is a mathematical tool to deal with it logically and numerically .

MIT multi variable course explains it very very well i advise you to watch it :)

Hello Abdulrahman Mohammed !

Electric flux, property of an electric field that may be thought of as the number of electric lines of force (or electric field lines) that intersect a given area. Electric field lines are considered to originate on positive electric charges and to terminate on negative charges. Field lines directed into a closed surface are considered negative; those directed out of a closed surface are positive. If there is no net charge within a closed surface, every field line directed into the surface continues through the interior and is directed outward elsewhere on the surface. The negative flux just equals in magnitude the positive flux, so that the net, or total, electric flux is zero. If a net charge is contained inside a closed surface, the total flux through the surface is proportional to the enclosed charge, positive if it is positive, negative if it is negative.

The mathematical relation between electric flux and enclosed charge is known as Gauss’s law for the electric field, one of the fundamental laws of electromagnetism. In the metre-kilogram-second system and the International System of Units (SI) the net flux of an electric field through any closed surface is equal to the enclosed charge, in units of coulombs, divided by a constant, called the permittivity of free space; in the centimetre-gram-second system the net flux of an electric field through any closed surface is equal to the constant 4π times the enclosed charge, in electrostatic units (esu).

https://www.britannica.com/science/electric-flux

Electric Flux Density, D, is a conceptual/graphical vector field that we use to get a “feel” for a complicated electric field made by source charges; it ignores alternations made to the electric field caused by the presence of material objects. What is exactly an electric flux, as you ask, is called a flux line. A flux line represents the trajectory a positive test charge would take if placed at that point, or the force a positive test charge would experience if placed at that point.1 Flux lines aren’t real, they’re just useful for visualization, and the number of them that emanate from a charge is arbitrarily set; in SI units, 1 flux line will emanate from 1 C.2

I would also like to point out that the answer given by André Michaud is verbatim the definition of electric current, and must be a misunderstanding of your question.

1. From Introduction to Electrodynamics by Griffiths

2. From Elements of Electromagnetics by Sadiku