According to Wikipedia, "Steam is a digital distribution, digital rights management, multiplayer and communications platform developed by Valve Corporation." According to those of us that know, Steam is the virtual equivalent of a crack dealer who will take all of your money to provide you with fleeting moments of satisfaction and joy.
And right now it is their infamous Summer Sale! Between now and July 22nd a buttload of games are reduced, with many being slashed even further for limited periods along the way. You can vote for games you want to be reduced, you can buy games for dirt cheap, you can gift them to other people, you can stock up on them until you create a backlog so huge you never want to open Steam and look at your game library again!
You can go to this handy website which shows games offered by Steam, listed in order of how much they are reduced. Go grab yourself a bargain!
You can also talk about other PC game stuff in here. But why would you want to! SALE SALE SALE!
Also Steam have started doing trading cards, which you can turn into badges, which you can turn into backgrounds and emoticons and stuff, which you can turn into ????? Because apparently buying and playing games isn't fun enough, now buying and playing games has to in itself become a game.
The regal and majestic Fyndir has created a handy spreadsheet so that people can more easily find and advertise cards. Which is pretty rad of him! It's right here so go use it you big nerd.