Slang term for cannabis/ marijuana originating in suburban southern Washington state. Refers specifically to flower/ bud, not processed concentrates or edibles.
Most likely the group of kids at your school who yell the word 'Gritch' all day and sing dumbass songs with the word 'Gritch' in it. Pronounce 'Gritch' 'gr-EECH' like 'gr' from 'great' and 'EECH' from 'leech'.