This is the flashing cursor on your computer screen (it looks like "|"), where you are supposed to type in something. You'll see the prompt when a host system asks you to do something and waits for you to respond.
For example, if you see "login:" and the flashing prompt, it means you should type your username. In most word processors, the prompt indicates where you are at the moment. name.
NetLingo Classification: Online Jargon