They can be compared with gradable adjectives, which have different degrees and so can be graded.
Example
‘Enormous', ‘impossible' and ‘ridiculous' are non-gradable adjectives.
In the classroom
Learners can explore non-gradable adjectives and have fun discussing things they think are absolutely disgusting, totally unbearable, utterly unbelievable, etc.
See also:
https://www.teachingenglish.org.uk/article/gradable-adjectives
Further links:
https://www.teachingenglish.org.uk/article/presenting-vocabulary
https://www.teachingenglish.org.uk/article/collocation-advanced-levels-1-not-entirelyproperappropriategood