Quota
Also called quota sampling, quota cell
A cap on how many responses you will accept for a segment, so one group cannot fill the whole sample.
Eligibility and quotas answer different questions. Eligibility says who belongs in the study at all; a quota says how many of a particular kind you will collect. Set them around the analysis you intend to run: if you plan to compare three regions, each region needs enough responses to compare, which is a decision about cells rather than about totals.
Quotas make a sample's composition look like the population without making it random. That is a real improvement over whoever answered first and it is not the same as probability sampling, so the margins and tests remain approximations.
When a cell fills, the people who arrive next need a clear ending, not a broken survey. Decide what that screen says before it appears to somebody.
Where it goes wrong
Plan the sample size for each comparison you intend to make. The total response count can hide small groups with imprecise estimates.