To broadcast is to air a program, especially on TV or radio. It also means to tell people about something. If you paint your one true love’s name on your car, you broadcast your feelings to the whole world!
The word broadcast used to have to do with spreading seed, but now it refers to spreading information. It can be a noun or verb — if you turn on the radio, you're hearing a broadcast, and the station is broadcasting that show. You don’t have to be in a studio to broadcast, though. Any time you let a lot of people know about something (whether they like it or not), you broadcast. When information is broadcast, it becomes widely known.