# Operator glossary

> Terms used consistently across identity, analysis, advice, and evidence fields.
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| Term | Meaning in this atlas |
| --- | --- |
| **Active foreground session** | A client-facing backend with `state = 'active'`; background main loops are excluded from contention percentages. |
| **Snapshot share** | The fraction of sampled active foreground sessions on one event. It is a triage signal, not elapsed-time attribution. |
| **Wait identity** | Exact `(wait_event_type, wait_event)` spelling observed in a release. Renames remain separate matrix rows. |
| **Canonical event** | One semantic dossier that can consolidate explicitly verified historical spellings or type moves. |
| **Trigger** | The source path that passes a wait-event identifier to PostgreSQL's wait reporting machinery. |
| **Catalog definition** | A source row that defines the public name/description. It is not automatically proof of a live trigger. |
| **Dormant event** | A catalog identity with verified negative source evidence: no live core reporter in the audited patch release. |
| **Heavyweight lock** | SQL-visible lock-manager object, normally diagnosable through `pg_locks` and `pg_blocking_pids()`. |
| **LWLock / tranche** | Short internal lock protecting shared-memory state; the tranche supplies the displayed event name. |
| **SLRU** | Small shared cache and on-disk segment set for transaction-related metadata such as pg_xact and multixact. |
| **Buffer pin** | A backend's temporary claim that a shared buffer page must remain present and structurally stable. |
| **Source release** | Exact audited tag, such as `REL_18_6`; line numbers are never attached to a drifting stable branch. |

Advice thresholds in this site are operational defaults. PostgreSQL does not promise that “10%” or “five seconds” is universally bad; use the cluster's own baseline and service objectives.