What does "liquidity" mean in a basic economic terms?

I am 23 and have gone through a financially turbulent life since graduating, therefore I decided to research, study, and learn as much as possible about personal finance and general economic theory in order to improve my habits and understanding. One word I heard/read often is “liquidity” and while I’ve read a few definitions, I feel I have yet to comprehend the term and its modern applications. I would appreciate any advice. Thank you.