Adverbs of degree tell us the strength or intensity of something that happens. Many adverbs are gradable, that is, we can intensify them. Basically they answer the sort of question that asks How much ...? or How little...?

Adverbs of degree include; adequately, almost, entirely, extremely, greatly, highly, hugely, immensely, moderately, partially, perfectly, practically, profoundly, strongly, totally, tremendously, very, virtually etc.

For example:-

The man drove badly. = The man drove really badly. - In this sentence really shows us just how badly he drove.
They enjoyed the film. = They enjoyed the film immensely. -
In this sentence immensely shows us how much they enjoyed the film.

These intensifiers are not gradable though, you cannot say The man drove extremely very badly.