What's the difference between a LCD projector lamp and bulb?

In my clroom, the LCD projector image says, "Replace lamp". As of now, I can use it, but a yellow light is blinking on the projector, so I"m not sure how long it will last. Of course our head custodian is gone (for a good reason) and no one else knows what that means. What exactly does "replace lamp" mean? My bulb burnt out about a month ago, so that should still have lots of life left in it. Thanks!