[gassiss]

it's at least one server (_any_ computer that never turns off) hosting things you would use (and probably pay) on a day-to-day basis.

The most important point is to be available all the time in multiple devices that you own, that's why some folks don't want to do these things on their main machines. A laptop you could take it away, and your family at home would/could lose access to the things you're hosting. A beefy desktop might be a bit too power hungry to be on all the time.