Finestra spell

Finestra was the incantation of the spell which shatters the glass of the target window into dust, allowing people to walk over the shattered pieces without damage.

Newt Scamander shattered the front window of the Voclain & Co. jewellery store in New York using this spell when he discovered his escaped niffler loose inside the store and wanted to try to recapture it. The window soon reappeared and became adhesive, sticking the Niffler to it like a fly on spider web.

Etymology
The word finestra means "window" in Italian, Catalan and Sicilian. Given Rowling's use of puns in the construction of other incantations (e.g. Orchideous and Aguamenti), it is also possible that finestra is a sort of double entendre - a humorous blend of fine or finis, the Italian and Latin words for "end", and finestra for window. Taken together, this could allude to the spell's ironic capacity to destroy windows in the creation of an opening or "window".

Notes and references
Finestra