To inform someone means to give them facts or knowledge about something. When your teacher informs the class that tomorrow's field trip has been canceled due to rain, she's sharing important information you need to know. When a newspaper informs readers about events happening in their city, it's providing facts so people understand what's going on.

Before you're informed about something, you might be confused or unaware. Afterward, you have a clearer picture.

Being informed (the adjective form) means having good knowledge about a topic. An informed citizen keeps up with news and learns about issues affecting their community. An informed decision is one you make after learning the relevant facts, not just guessing or going with your gut feeling.

You can also inform on someone, which means telling authorities about something wrong they did. This phrase often suggests tattling or betrayal, though sometimes informing authorities is the right thing to do, like when someone's safety is at risk. Someone who regularly informs on others to the police might be called an informant or, more negatively, an informer.