I think that you are referring to the energy conversion factor was used in the past to make equivalent the two energy transfers: heat and work.

In fact, at the time, the first principle of thermodynamics was written in the form

DELTA U = Q - J L

where U is the system internal energy, Q the exchanged heat, J the conversion factor (energy conversion factor) between Joule (work L) and kilocalories (heat).

In fact, it was assumed that U and Q had to be measured in kilocalories while L was measured in Joules.

However, since in a formula all the summed up quantities must have, not only the same dimensions, but also the same measuring units, it was later decided to drop the J and to write more simply:

DELTA U = Q - L

In M,L,T,t system the dimension of energy (you can derive it from either U, or Q, or L) is:

L = Force x Length = Mass x Length x Length / (Time x Time)

Finally 1 kilocalorie = 4186.8 Joules, number which is the reciprocal of J if you measure U and Q in kilocalories and L in Joules.