Letters that make pop-up
o, p, u are letters that make 'pop-up'
2 possible definitions for 'pop-up'
Under this definition, pop-up is a noun and has the following properties:
pop-up book has the same meaning as pop-up
'pop-up' can be a type of book.
Under this definition, pop-up is a noun and has the following properties:
'pop-up' can be a category of baseball, baseball game.