Term: "Heightening/Upcasting a spell..."

'Heightening' a Spell just means increasing a spell's strength by ⤴/Augmenting Upward.

It is a classic use of the term that other games use, while CHASE's differentiation comes from the ability to 'Downcast' or ⤵/Augment Downward, as well as other means of altering an ability's strength.