The breeding of people/ animals/ plants that are closely related to each other (first cousins or even closer), thus keeping the genepool weak and leaving them vulnerable to various health problems, mentally and emotionally as well as physically.
Purebred dogs and royalty are notorious for inbreeding; to keep the line "pure" then they are only allowed to procreate with their "own kind", even when offspring are stupid, sickly, deranged, ugly or any number of things.

Carlos II of Spain was the end result of the Spanish Hapsburgs; his parents were uncle and niece and both were highly inbred. Carlos was deformed, retarded, delicate, and had an extended infancy and premature senility. He was married twice, but he was impotent and sex was beyond his abilities.

Plants can be inbred, too; bananas of today are very different from those of three generations ago and often lack the genetic diversity which would keep them healthy.
by Lorelili January 16, 2011
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The breeding of two animals who are related to each other.
by M February 19, 2004
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How graduates and fans of Auburn University (a.k.a Cow College, The Barn, Bama Poly, The Silo, Redheaded step-child) procreate.
EaglesKill05 practices inbreeding with his mother. The result is a child with huge ears, 12 toes, 8 fingers, and no balls.
by Roll Tide Roll October 20, 2005
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A person who has sex with their own relatives or family members. The term usually refers to one who has sex with their siblings.
Why are you looking at your sisters butt? Are you an inbreeder or something?
by tory borty September 2, 2013
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1.) The lowered overall fitness of a population due to reproduction between closely related individuals, thereby lowering heterozygosity in the population and allowing deleterious alleles to be expressed.

2.) The crushing guilt that follows fucking your sister.
Inbreeding depression is a serious risk in small populations.
by SimpHawk September 20, 2018
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Groups of people who conspire to believe in the same myths.
There's an awful lot of psychological inbreeding going on over at /r/conspiracy.
by Professor Duskull July 5, 2017
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A condition caused by homeschooling in which an individual is around their immediate family for so long that it causes a severe lack of diversified social input.

The condition is analogous to normal inbreeding which causes a severe lack of genetic input.
-"Hey, have you met that John guy who's really clingy and talks like an old church lady?"
-"Oh yeah, he doesn't have a sense of humor and he's afraid of his own penis."
-"Guys, don't make fun of John...he's socially inbred because his hyper-religious mom homeschooled him."
-"Some Mormon kids down the street from me were all messed up from social inbreeding. They were like children of the corn, only creepier."

-"I saw him kiss his mom on the mouth."
by LooseLucyCat February 16, 2011
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