An adverb is a word or set of words that modifies or describes verbs, adjectives, or other adverbs.
- The bulb in the room has been glowing continuously.
- We ran fast to catch the bus.
- Thank you very much for your cooperation.
- Their work was almost complete.
- Your story is quite interesting.
In sentences 1 and 2, continuously and fast modify the sense of the verbs glowing and ran, respectively. In sentence 3, very modifies the sense of the adverb much, while in sentences 4 and 5, almost and quite add to the meanings of the adjectives complete and interesting, respectively.
Hence, continuously, fast, very, almost and quite are adverbs.