jatinarora97:
It's not that clear cut, but hopefully this helps:
There are tiers of schools mostly based on perception and historical ranking, and even these are somewhat subjective, especially with the lower tiers.
Tier I: Harvard, Stanford, Penn (Wharton)
Tier II: MIT, Columbia, Northwestern (Kellogg), Chicago (Booth)
Tier III. Yale SOM, Michigan, Berkeley (Haas), UCLA, Duke, Dartmouth (Tuck), NYU (Stern), Virginia (Darden)
Tier IV: Cornell, Georgetown, Texas (McCombs), Carnegie Mellon (Tepper), USC (Marshall)
That gets you to 20. Of course, you could make an argument to put other programs, such as UNC (Kenan-Flagler) and Washington (Foster) in there. Emory (Goizueta), Vanderbilt (Owen), Rice (Jones) Indiana (Kelly), and Notre Dame (Mendoza) are also very excellent programs that could round out the 20, especially if you start talking about particular areas of focus (e.g., finance, management, operations, etc.)
That's why people often refer to M7 (Tiers I and II), and T15 (Tiers I, II and III). Thereafter, it's very hard to categorize a school as definitively in T20, T25, T30. At that point, it simply doesn't really matter. It's just subjective labeling.