Definition
Passage ranking is the technique (introduced by Google in 2020, now used by all major retrieval engines) of indexing and ranking individual passages within a long page separately from the page's overall ranking. A 5,000-word guide can have its 'pricing' passage rank for pricing queries even if the whole page ranks for the broader topic. AI engines exploit this aggressively: they extract specific passages, not whole pages, for citation.
A complete guide to AEO with sections on 'definition', 'history', 'tools', 'pricing'. Each section can independently rank for queries matching its topic.
How to optimize
Use clear H2 boundaries between sub-topics. Make each section self-contained (don't reference 'as discussed above'). Add anchor links to each section.