An adverb is a word that gives additional information about an action or idea. They fall into several categories:

Category Example
manner carefully; slowly
frequency always; often
time and place now; here
relative time already; recently; soon
degree extremely; rather; very
quantity a lot; a little
focusing even; also; only; particularly
marking attitude apparently; fortunately

Source: Grammar for English Language Teachers p.29 (c) Cambridge University Press.

» 7.1 Glossary - Key language concepts