Wickard v. Filburn was a Supreme Court case that had to do with the extent of Congress's power to regulate interstate commerce. In this case, the Court granted Congress extensive powers in this regard.
The law in question was the New Deal program known as AAA. Under this law, the government specified how much of certain crops farmers could produce. Filburn produced more wheat than he was supposed to and sued when he was fined. He said that the wheat was for consumption on his own farm and therefore had nothing to do with interstate commerce. The Court ruled unanimously that the wheat did affect interstate commerce even if it never actually entered the stream of interstate commerce. This was because any excess wheat produced by Filburn and others like him reduced overall demand for wheat in interstate commerce.
Overall, then, this is a case about how much Congress can intervene in the economy using its power to regulate interstate commerce.