English staff incorporate special gap in text (2,5)

'gap in text' is the definition.
(space as wide as a letter 'm')

'english staff incorporate special' is the wordplay.
'english' becomes 'e' (abbreviation).
'staff' becomes 'mace' (a mace is a ceremonial staff or stick).
'incorporate' means one lot of letters goes inside another.
'special' becomes 'sp' (abbreviation).
'mace' placed around 'sp' is 'mspace'.
'e'+'mspace'='EM SPACE'