The phrase "top quintile" refers to the highest fifth or 20% of a group or population. It means being among the top performers or earners in a specific category. Full definition
In Tennessee, the most effective programs produced graduates who were 2 - 3 times more likely to be in top quintile of teachers in the state, while the least effective programs produced graduates who were 2 - 3 times more likely to be in the bottom quintile. (apluscolorado.org)
With the bottom - top quintiles paying an Effective Federal Tax Rate (EFTR) of 1 %, 6.8 %, 11.1 %, 15.1 %, and 23.2 % respectively. (politics.stackexchange.com)
Finally there's access to elite colleges that cement the grip of top quintile families on the brass ring of their advantage. (educationnext.org)