Is this true or false an extinct animal is one that lived in the time of the dinosaurs?

It is true that most animals alive during the time of dinosaurs are now extinct. However, any animal can go extinct, even in modern times.

For instance, the pallid beach mouse went extinct in 1959. The Pyrenean ibex went extinct in 2000. The eastern cougar went extinct in 2011.

Extinction simply means there are no animals of that type left. They have all been wiped out through hunting, deforestation, illness, or other reasons.