Definition
Doorway pages are pages produced primarily to rank for a keyword and funnel traffic to a canonical destination, typically with thin or duplicated content. Google's quality guidelines have banned them since 2015.
Why it matters
The failure mode of naive pSEO is producing doorway pages by accident, swap a city name into a template, change nothing else, and you have 50 pages that Google will collapse into one or penalize outright.
How we think about it
We treat the doorway line as a hard CI gate. Every pSEO page has to pass a 40% n-gram difference check against every other page in its set, carry 500+ words of unique body content, and include a distinct FAQ block. A set failing the gate blocks the merge, not the reverse.