An eventtype is a search that runs when you specify eventtype=MyEventType; you can think of it like a "pipeless, parameterless macro" or even like a saved search.
A tag is a not-necessarily-unique "nametag" given to a specific, definitive (wildcardless) Key-value-pairing. It is very much like an eventtype but it has the following differences:
An instance of an eventtype name is defined by a single directive inside a single eventtypes.conf file but an instance of a tag name can be defined in an infinite number of separate tags.conf files.
An eventtype definition can use wildcards and have any number of pre-pipe specifications (conjunctions) but a tag definition always contains a single key=value pairing.
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