The National Tennis Rating Program is the USTA's playing-level classification. Its general descriptions run from 1.5 to 7.0 in half-point steps; adult leagues commonly use levels from 2.5 to 5.0.
A rating groups similar abilities; a ranking orders players by competitive results. Players at the same rating can still have different strengths.
In Korean recreational tennis, NTRP is often an informal reference rather than an official USTA classification. Judge yourself by recent match results and repeatable skills, not years of lessons or your fastest shot.