There is no single meaning, but is used to convey a casual sense of affirmation, acknowledgement, said in agreement, something that is real, absolute, well said, a person dropping mad knowledge while unconsciously projecting who they are onto others and exposing him or her self as a hypocrite.

Or to indicate that something has impressed you favorably but everyone really knows the person doing the preaching is clueless and talking out of their ass.

Its usage among young blacks has been parodied ad nauseam among clueless suburban whites who actually do have a clue and calling out their counterpart who are the ones who actually have no clue.
Schnoup says... "man, what an ignorant piece of trash..."
Dawg's response... "preach..."

Elmer... "You are the one who obfuscates damn near everything, so you can soothe your self-righteous ego. You like to do that, so you can twist the conversation back to your positions and try to put the others on the defensive. Few exceed your mastery of that kind of arrogance - truly."

Fudd... "preach."
by theycallmepseudonym January 12, 2014
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It means sure, which is used widly used by Snoop Doggie Dog.
-Yo man, let's go get some KFC!
- Preach
by MarkoE500 December 11, 2006
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good look or a statement that agrees with what was previously said
Fuck Tha world ...Preach
by ruckus March 15, 2004
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Social media driven 'wank-speak' for when another cretin that is like you says something you agree with.
'like, bro.. did a mad trap tune'

'like, bro.. preach it...youll get loads of likes'
by tom healey September 13, 2016
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to have somebody speak up about a subject with an opinion that is very common and isn’t afraid to repeat it (they’re a preach)
Donald Trump is a nonce

Donald Trump is racist
by memeulousisverylarge June 09, 2020
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Saying amen and praising an action you have done. Or hyping someone up.
Person 1: My house is on fire lol.
Person 1: Amen!
by Noah beck neck (what the heck) November 29, 2020
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