An instantaneous wind is just that, the wind at that instant. As Gonzo said, we usually use the 2 min average unless sepcifically asked for an instantaneous reading. We use a 10 min average for the METAR report, which goes out on the ATIS.
A gust is defined by the Met. Office as a maximum wind speed over the corresponding 10 mins which exceeds the mean by 10 kts or more. Don't think I've seen a definition (in the UK) of a peak wind
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VA
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