from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A child.
- n. A young person.
- n. Slang Pal. Used as a term of familiar address: "I said to the girl, rather snootily: 'I have a trade, kiddo. I'm a detective'” ( Ross Macdonald).
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. An affectionate moniker for a close friend or pal, especially used as a form of address.
Probably derived from kid, an informal term for child. Appears to be colloquial in United States and Canada. (Wiktionary)