The English word for vacation is holiday.
And the month of May is like pre-summer holiday. 3 of the 4 weeks have jours ferié. That means May 1, 6, 8, 9, 19 & 20 are all off. And the French generally fait le pont (fay leu pohn make the bridge).
So the 8 & 9, add the pont and you have a 5 day weekend.
Nothing happens in Paris in May. Much like July & August. But unlike July & August, May usually has good weather. Sadly - May has forced le sigh out of my mouth more than once. See this