Full Idea
A formula is said to be in 'prenex normal form' (PNF) iff all its quantifiers occur in a block at the beginning, so that no quantifier is in the scope of any truth-functor.
Gist of Idea
'Prenex normal form' is all quantifiers at the beginning, out of the scope of truth-functors
Source
David Bostock (Intermediate Logic [1997], 3.7)
Book Reference
Bostock,David: 'Intermediate Logic' [OUP 1997], p.109
A Reaction
Bostock provides six equivalences which can be applied to manouevre any formula into prenex normal form. He proves that every formula can be arranged in PNF.