EC2 are cloud based virtual machines, very easy to spin one up exactly as you need it to run whatever.
But they're billed hourly and they get very expensive very very fast especially when you leave it on (the hourly billing is for a machine that's on and running) and have shit tons of resources on it. You can have multiple terabyte RAM machines at the click of a button
Amazon charges per hour for renting a server. Some are very expensive. It’s a common mistake to forget to turn off a server after you’ve finished using it and end up paying more than you planned.