What exactly is a stalemate? I searched it up but I'mm kinda confused.

A stalemate is a period during war where the opposing forces cannot progress (this is in terms of both a 'hot' or a 'cold' war). For example, during WW1 there was a stalemate on the Western Front due to advanced defenses built by the Allies and the Central Powers. This meant that new offensive tactics and strategies had to be employed in order for either side to gain terrain. The trench warfare system that brought about the stalemate of WW1 was triggered by the failure of Germany's Schlieffen Plan.