What does freeware mean?
This one is easy. A freeware game is a game available for free, no payments are necessary. It may seem a little strange to someone used to buying games on Steam (maybe during Steam sales...), that the internet is already stuffed with A LOT of completely free video games, but it's true!
Not every free game is a high quality game, we're talking about software often developed by a single person, maybe as a way to learn a new programming language, so a lot of free games are, well... there's no other way to put it... plain horrible, but you have to respect the effort. After all, you are not paying a dollar (or an euro, or pound, or... whatever).
There are also some free-to-play video games that you can download and play right away but are filled with optional content that you can buy. There is a subtle difference between completely free and free-to-play games, learn more about free-to-play games on Free Games Utopia, an affiliate of Abandonware DOS.
Last but not least, freeware doesn't mean that you can do anything with it. For example some freeware games can't be re-distributed without the owner's permission.