An ELT Glossary : Correlatives

Correlative expressions consist of two parts. They may belong to various word classes. 
Some examples :

Correlative conjunctions - eg either/or,  neither/nor,  both /and,  not only/but also,  
if /then etc
She not only got 100% on the test,  but also finished in half the time allowed.
If he refuses, then we'll need to change our plans.

Correlative prepositions - eg   from / to,   between/and
We're open from 9 to 5.
I'm not sure how old he is - but somewhere between 60 and 70, I think

Correlatives may also mix word classes as in the expression as (adv) / as (preposition)
He's as stubborn as a mule.