i will add a better definition later but to me a Classic is when you don't have to skip tracks on a album to get to the next track,i came from the cassette tape era so you wanted to put in something that you could ride to straight through without having to fast foward and here is a few classics.
Note that: these are more on the mainstream but 10/10 albums

Havoc & Prodeje - Kickin Game
Lynch - Season of the Siccness
Mr Doc - Set'rippin
Bone Thugs - Creepin on a comeup
ESG - Sailin Da South
ATL - Uncle sams curse
Eiht - We come Strapped
Rodney O & Joe Cooley - me & joe
Crime Boss - All in the game

i will add more later and give my 2 cents on Classic

Straight up though the most CLASSIC album of ALL time in my opinion is RUN - D.M.C - Run - D.M.C. [1984] that album is sentimental to me plus it's a banger all the way through.