⟨NNBSP⟩
Thin and welded: the space French demands before the exclamation mark.
French typography calls for a blank before !, ? and ; and inside guillemets — but a blank that can neither become a line break nor be wide. The narrow no-break space is that gem: thin like U+2009, welded like U+00A0.
It is also the recommended thousands separator: 1 000 000 will not part at the end of a line. No named entity — you call it  .
Wrong: Bonjour ! — the ordinary space lets the mark fall alone
Right: Bonjour ! — narrow and welded, as French demands