Polyglot derives from the Greek term polyglōttos which, roughly translated, means ‘many-tongued’ is someone who speaks a lot of languages fluently. There is no official number of languages you have to know to be a polyglot , but it’s usually at least four or five languages.
A linguist, on the other hand, is someone who studies languages. There are different fields of linguistics, such as phonetics, phonology, morphology, typology, semantics, pragmatics, and syntax. The point of linguistics is to study human languages, not learn as many languages as humanly possible.
So if you ever meet a linguist, don’t immediately ask them how many languages they speak because it's like asking a biologist how many pets that they have.