noun

used to refer to something which is boring or without meaningful content.

the first 20 pages are a lot of blah about budgets and stuff like that

adjective

dull or unexciting.

the game has been very blah

exclamation

used to substitute for actual words in contexts where they are felt to be too tedious or lengthy to give in full.

he said nations great and small could come together to blah blah blah