What is a pun?

Examples:

1. Two antennas met on a roof, fell in love and got married. The ceremony wasn't much, but the reception was excellent.
2. A jumper cable walks into a bar. The bartender says, "I'll serve you, but don't start anything."
3. Two peanuts walk into a bar, and one was a salted.
4. A dyslexic man walks into a bra.
5. A man walks into a bar with a slab of asphalt under his arm and says: "a beer please, and one for the road."
6. Two cannibals are eating a clown. One says to the other: "Does this taste funny to you?"
7. "Doc, I can't stop singing 'The Green, Green Grass of Home'" "That sounds like Tom Jones Syndrome" "Is it common?" "Well, "It's Not Unusual."
8. Two cows are standing next to each other in a field. Daisy says to Dolly, "I was artificially inseminated this morning." "I don't believe you," says Dolly. "It's true, straight up, no bull!" exclaims Daisy.
9. An invisible man marries an invisible woman. The kids were nothing to look at either.
10. Deja Moo: The feeling that you've heard this bull before.
11. I went to buy some camouflage trousers the other day but I couldn't find any.
12. A man woke up in a hospital after a serious accident. He shouted, "Doctor, doctor, I can't feel my legs!" The doctor replied, "I know you can't - I've cut off your arms!"
13. I went to a seafood disco last week...and pulled a mussel.
14. What do you call a fish with no eyes? A fsh.
15. Two fish swim into a concrete wall. The one turns to the other and says "Dam!"
16. Two Eskimos sitting in a kayak were chilly, so they lit a fire in the craft. Unsurprisingly it sank, proving once again that you can't have your kayak and heat it too.
17. A group of chess enthusiasts checked into a hotel and were standing in the lobby discussing their recent tournament victories. After about an hour, the manager came out of the office and asked them to disperse. "But why," they asked, as they moved off. "Because", he said, "I can't stand chess-nuts boasting in an open foyer."
18. A woman has twins and gives them up for adoption. One of them goes to a family in Egypt and is named 'Ahmal'. The other goes to a family in Spain ; the y name him 'Juan'. Years later, Juan sends a picture of himself to his birth mother. Upon receiving the picture, she tells her husband that she wishes she also had a picture of Ahmal. Her husband responds, "They're twins! If you've seen Juan, you've seen Ahmal."
19. Mahatma Gandhi, as you know, walked barefoot most of the time, which produced an impressive set of calluses on his feet. He also ate very little, which made him rather frail and with his odd diet, he suffered from bad breath. This made him. A super calloused fragile mystic hexed by halitosis.
20. There was the person who sent twenty different puns to his friends, with the hope that at least ten of the puns would make them laugh. No pun in ten did.

pun
Pronunciation noun, verb, punned, pun·ning.
–noun

1.the humorous use of a word or phrase so as to emphasize or suggest its different meanings or applications, or the use of words that are alike or nearly alike in sound but different in meaning; a play on words.

Example:
“The body builder worried too much about the lifting contest and his trainer concluded that the mind is a terrible thing to weights.”