Gradable adjectives are adjectives which have different degrees and so can be graded. They can be compared with non-gradable adjectives, which do not have degree.
‘Hot' and ‘cold' are both gradable adjectives. You can say ‘very hot', ‘a bit cold' ‘really hot', ‘rather cold' etc.
In the classroom
Learners find focusing on collocations such as ‘absolutely awful' and ‘a bit chilly' interesting, and this is a natural way to focus on whether adjectives are gradable or not. It may not necessarily be useful for learners to spend time separating adjectives into gradable and non-gradable, as this will not immediately help them use adjectives correctly.