What's the difference between a trill and a mordent?

[d̗̰̗͆͘ǎ͔̱͈̰̬̫ͨ̌ͮͥ͗ͭ̕vid]

For a trill, do I hit the bottom note multiple times, while for a mordent, only once? Or does it just vary?

Thanks,
David