Pun

A pun [puhn] is a play on words.  It is a figure of speech, using a word humorously to suggest different meanings at the same time.  At our house, we call puns
"Grandpa Rick Jokes".  My dad is the king of bad puns, and has always loved punishing us with his silly humor.  We groan when he tells his jokes, but we laugh, too -- and I've discovered over the years that I enjoy making up puns myself!

The best puns play on both sound and meaning.  Here are a few that made me giggle when I found them online:

I'm reading a book about anti-gravity.
It's impossible to put down.

I was going to look for my missing watch,
but I could never find the time.

I did a theatrical performance about puns.
Really it was just a play on words.

Time flies like an arrow.
Fruit flies like a banana.

There was a man who entered
a local paper's pun contest.
He sent in ten different puns
hoping at least one of the puns would win. 
Unfortunately, no pun in ten did.

If you'd like to see more fun examples, check out this Pun of the Day website I came across.  What are some of your favorite puns?