[BruceIV]

Take the analogy from natural languages, and you're fluent in any language where you can write simple programs without consulting the documentation (or only minimal consultation), conversant in any language you can get real work done in, and speak broken language X if you know Hello World and not much more.

A polyglot should be fluent in multiple languages, from at least a couple different families, and conversant in many more.

[cgag]

What it means to be "fluent" in a natural language is probably even more disputed than with programming languages. It is a good metaphor in that sense though.

[SkyMarshal]

Fwiw, I've always understood "fluent" and "conversant" to be the opposite of above - "fluent" being the highest level, indistinguishable from a native speaker (slang, dialect, accent all spot on), while "conversant" means able to communicate and get along but obviously it's a second language to you.

I don't doubt linquists dispute something like that though.

[BruceIV]

"Fluent" has a rather vague definition, but the word root means "flowing" (like a river) - if you can speak a natural language in proper idioms without pauses in the wrong places to look for or translate words, you're fluent. "Conversant" is a rather lower standard meaning that you can have a conversation in the language and both understand and be understood.

[cgag]

Same here. I would never call myself fluent in Spanish, but then I've seen people on my level or worse who do and it's frustrating. I've seen plenty of similar arguments online about what it means to be fluent.

[kermitten]

"Conversant in any language you can get real work done in", I think this is a pretty good baseline to define if you know a language or not. :)