Latin adage meaning Times change.
Occasionally a longer version is used: Tempora mutantur et nos mutamus in illis, i.e., "Times change and we change in them.
An interesting observation for the student of the subtle: The "mutantur" is passive, i.e., literally, Times are changed, or perhaps Times are subject to change.
On the other hand, "mutamus" is active, that is to say, "we change", not "we are changed", nor "we are moved to change because of changing times."
Indded, times change because we do, not the other way. Though some of us need a kick in the pants. But the adage expresses the idea that times change because of us.
If you need a mnemonic to remember this, think of New York Times: It describes the society in and out of New York. As the society changes, so does the content of New York Times. This is a bad pun, which is why it is a good mnemonic.