What causes "RAM leaks"?

[Midnightas]

I am writing a simple game in ez80 assembly, and every single time I run the program, my calculator's free RAM goes down a lot.
I can run the game maybe 4-5 times before it runs out and a memory error occurs.

Is my program simply not deallocated from memory, if so, how do I get it to?

[Midnightas]

It turned out to be me setting IY without saving the old value.

[rowan_futurerave]

I'm not sure about assembler, but in C and C++ memory leaks are caused by using the calloc/malloc routines (in C) or the new operator (in C++) without using corresponding calls to free (in C) or delete (in C++).