> ## Documentation Index
> Fetch the complete documentation index at: https://wiki.platelunchcollective.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Topic Coherence

> Topic coherence is the degree to which all content within a chunk or section addresses the same underlying topic.

*Core concept* · *AI Search Infrastructure*

## Definition

Topic coherence is the degree to which all content within a chunk or section addresses the same underlying topic. High topic coherence produces tight embeddings that retrieve consistently for their target sub-query. Low topic coherence produces diffuse embeddings that retrieve weakly across multiple sub-queries.

## Why It Matters for AI Search

Topic coherence is the content-side property that determines embedding quality. Research confirms that explicitly incorporating topic structure into embedding construction reduces retrieval of off-topic chunks by statistically significant margins — and that the penalty for low-coherence passages increases as embedding models improve. The models are getting better at detecting it, not worse.

## Related Terms

<CardGroup cols={2}>
  <Card title="Semantic center of gravity" href="/ai-search-glossary/semantic-center-of-gravity" />

  <Card title="Embedding drift" href="/ai-search-glossary/embedding-drift" />

  <Card title="Semantic density" href="/ai-search-glossary/semantic-density" />

  <Card title="Vocabulary effect" href="/ai-search-glossary/vocabulary-effect" />

  <Card title="Cluster" href="/ai-search-glossary/cluster" />
</CardGroup>

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