Random access memory(some will say read access memory), it's where your cpu stores the next command for what your cpu is about to do( or your gpu if it doesn't have enough of it's own). The more, the better. Clearing ram, if done the wrong way, will be over time, detrimental to your system, it can clear something that wasn't supposed to be cleared, especially in android, windows works a diffrent way. Be careful when you see a ram clearing app, I use cache cleaners, they're safer.