I think what they man is 'peak of the waveform — i.e. when the AC voltage waveform is at a maximum; this contrasts with the 'zero-crossing switching point' normally desirable under operational conditions.

But this way of expressing it in EN is decidedly odd, and I am suspecting a non-native writer!

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Note added at 9 heures (2016-06-24 12:43:19 GMT)
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In that case, I am even more confident of my interpretation, that this is the instantaneous (rather than long-term) peak point on the voltage waveform

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Note added at 9 heures (2016-06-24 12:50:56 GMT)
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Asker, there is a subtle but very important technical difference here, which requires detailed specialist knowledge to fully appreciate. Be very wary of falling into the trap of using a 'common' but ultimately unsatisfactory solution purely for the sake of expediency.

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Note added at 4 jours (2016-06-28 10:28:15 GMT)
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Asker, your additional context confirms that this is precisely what I'd originally assumed, despite the flawed EN.

It is very important to diofferentiate between the INSTANTANEOUS peak point in the sinusoidal cycle, at single-cycle level — where it is the point in time during the cycle that is important; and the LONG-TERM peak value of the actual voltage, which in technical EN differentiates from, e.g., the rms value. Here, it is not the actual AMPLITUDE of the waveform that is important, but the point in its cycle at which it reaches its maximum (or zero, etc.). This may appear to be a very subtle technical point, but believe me, to anyone in the know, the distinction is VITAL!