Top Law Schools

I've seen some common terminology on TLS that I wasn't aware of so wanted to get some insights.

1. When referencing law schools, people typically use terms like T1, T2, T3 etc. I'm assuming these refer to tiers? Which schools would fall under these tiers? Are these determined solely by ranking?

2. When people post their own stats to get chanced for law school admissions, I've seen terms like T, TT, TTT, and TTTT when describing their undergrad school and a percentage such as "top 20%" or "top 30". Are those T's also tiers for undergrad? If so, how are they determined? I'm also guessing the percentage is referring to how they placed in their graduating class for their undergrads?

T1 refers to law schools with a USNWR ranking between 14/15-50 (or, sometimes, between 20-50, depending on the poster and the context). T2/TT = schools ranked 51-100, T3/TTT = 101-150, and T4 = the rest of the ranked schools, 151+.

The top law schools are referred to as the T13/T14 (top 13 or 14 law schools), and the T20 (schools ranked between 14/15-20; occasionally, T20 is used to refer to all schools 1-20). There is some debate whether the topmost category should include Georgetown (at 14) or end at Cornell (at 13).