Template:M summ 2021 ISDA Definitions 12.6.4

A mechanical provision governing how those Options that can be exercised in an interim fashion (namely, Bermuda-style and American-style Options) can be exercised. If the Confirmation specifies exercise Integral Multiples of a Notional Amount or specifies Maximum Notional Amount or Minimum Notional Amount, then you must comply with those on any exercise date, and if you don’t your exercise will be rounded down as appropriate (or cancelled if you are below the minimum).

None of this applies on the Expiry Date, at which point you may exercise to your heart’s content in whatever Notional Amount that may be remaining, as long as you exercise the whole lot.

Also, if less than the Minimum Notional Amount is left of the transaction at any time, you can exercise that whole amount on any Exercise Date.

It doesn’t apply to European-style Options because you can’t exercise them at any time before the Expiry Date, so you have to exercise the whole lot at once.