Lim, abbreviation for limit, used in Calculus and other advanced Mathematics.

The formula for finding a derivative is:

lim   f(x+h)-f(x)
h->0        h


The limit is used to evaluate what a function, sequence, series, et. al. is approaching as a certain variable, in this case h, approaches a certain number, in this case 0. Since a 0 in the denominator usually makes a fraction undefined, the limit is used to make it infinitely close to 0, or approaching 0, without actually reaching it.

Limits are essential to learning Calculus, and are the basis of further topics such as L'Hopital's Rule and Simpson's Rule.

And remember, the limit as x goes to infinity of 1/x is 0, but the limit as x goes to 0 of 1/x is infinity. What a crazy world we live in.