What is load effective address?

Load effective address, in assembler terms, and in the case of for example "lea eax, [esp-8]" means "please compute and put the address of [esp-8] into the register eax".

In other terms, "mov" works only on values, except you tell it to get the address of your source arg (you could do mov eax, offset [ebp-8]), while "lea" works on addresses only.