In the UK a 'pash' was a crush, usually of the non-sexual variety between a younger and an older girl or adult female. It's found a lot in the Enid Blyton type 'Mallory Towers' boarding school novels and usually described the relationship between a first year and a prefect or one of the 'Upper Fifth' form or a favourite teacher.

Anyone who uses it is immediately outed as a) a product of the early 1900's boarding schools, b) a closet Enid Blyton reader or c) a gym teacher.

LTS