Gazetteer
Around cartography, a gazetteer is analogous to a dictionary or encyclopedia - look up a location, and things about it.
They were seemingly introduced to know about parts of the world, and there were different types for different interests - e.g. broad world overview, to detailing parts of countries, to to almost tourist-like thematic information).
In some modern use it sometimes just means a name-to-coordinates lookup.
https://en.wikipedia.org/wiki/Gazetteer
Around computational linguistics, a gazetteer is largely just using a list of already known known names, probably per label/category you are interested in, and optionally some basic rules around it.
Around the task of Named Entity Recognition, this may provide good precision (a lot of names will be matched because we already knew them precisely), but poor recall in that unknown names, and e.g. variant spellings, will always be ignored.