Dear Padidela, 

Quite simply, the radial distribution is a type of particle distribution function. More precisely, the radial distribution function is the 2-particle distribution function. The n-particle distribution function may be written

g(n)(r1,..., rn) = ρ(n)(r1,..., rn) /Πi=1nρ(1)(ri)

If the system is isotropic, the two-particle distribution function g(2)(r1,r2) only depends on r= |r1-r2|, which is generally written as g(r) and called the radial distribution function. I recommend reading Hansen and McDonald's book (Theory of Simple Liquids (2nd edition), Academic Press, 1986), which gives an excellent introduction to particle distribution functions (chapter 2 from memory).

Hope this helps!

Cheers,

Quinn