What is a database transaction?

Question

Can someone provide a straightforward (but not simpler than possible) explanation of a transaction as applied to computing (even if copied from Wikipedia)?

Answer 1

In addition to the above responses, it should be noted that there is, at least in theory, no restriction whatsoever as to what kind of resources are involved in a transaction.

Most of the time, it is just a database, or multiple distinct databases, but it is also conceivable that a printer takes part in a transaction, and can cause that transaction to fail, say in the event of a paper jam.