I always think of the seasons in four increments of three months each -
Spring - March, April, May
Summer - June, July, August
Autumn - September, October, November
Winter - December, January, February
I know in this country, the weather can be wildly varied at pretty much any time of year; but, still, in terms of daylight hours etc, I think of the way described above.
I ask because a friend the other day described last weekend as summer. I said I see May as late spring. If we're having hot May days they're just hot spring days. We're back down to circa 12°C now, so the hot spell was short-lived; but I was curious to know how other people see it?