Definition of "informal" []

• Not formal or ceremonious; casual: an informal gathering of friends; a relaxed, informal manner. (adjective)
• Not being in accord with prescribed regulations or forms; unofficial: an informal agreement. (adjective)
• Suited for everyday wear or use: informal clothes. (adjective)
• Being more appropriate for use in the spoken language than in the written language. (adjective)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "V. i.236 (129,4) [These poor informal women] I once believed _informal_ had no other or deeper signification than _informing, accusing_."
• "I suppose you can call it "informal" -- we have a book club during the summers, and this year it was on Dinshaw."
• "Right off the kitchen was what she called their informal dining room."