A permanent ID is some opaque string, whose value will always represent the same OSM feature, such as a street, a building, a country outline, or a point of interest (POI). The ID must remain valid even if the country outline geometry is changed, a POI gets renamed, or if the street gets split into multiple segments — in this case the ID itself can’t group the segments, but generates a suggestion to group all with a relation that will preserve the ID instead the first segment.

The Permanent ID represents a “concept”

As editors improve data, any aspect of that data may change. A restaurant node POI may become a building or a relation, and its name may be corrected. A single way representing a street may be split into multiple ways due to a partial speed restriction, or may become two ways separated by a divider. The ID must still point to the original “concept”. Consequentially, not every OSM feature needs to have a Permanent ID.
This Permanent ID characteristic is closed with POI concept, linked data concept, “One feature, one OSM element” principle and the Wikidata-tag attribution process.

See also Persistent Place Identifier, and an implementation proposal.

Relation to IN COMMON

IN COMMON Resources use UUIDs to uniquely identify human and social geography markers. OSM PermanentID concept relates to geographical points of interest. IN COMMON Resources may be enriched with an OSM PermanentID to link the social layer to the geographical layer more precisely, especially when a Resource Location (e.g., latitude and longitude) matches more than one geographical feature on OSM, e.g., when referring to an area (e.g., a Polygon).