"A Nimbus Two Thousand, sir. And it’s really thanks to Malfoy here that I’ve got it."
-- Harry Potter (PS10)
The Nimbus 2000 is a high-end broomstick produced by the Nimbus Racing Broom Company. Harry Potter heard some boys admiring them in a shop window – “the new Nimbus Two Thousand – fastest ever” – during his first visit to Diagon Alley with Hagrid (PS5).
Harry’s first broom was a Nimbus 2000. Professor McGonagall arranged for him to receive one in his first year, as the Captain of Gryffindor’s Quidditch Team, Oliver Wood, felt that their new Seeker would need a good broom (PS10). At that time, the Nimbus 2000 was the best broom available. Harry used this broom until it blew into the Whomping Willow during a match against Hufflepuff in his third year and was destroyed (PA9).
The word nimbus most commonly refers to clouds that precede rain and is Latin for "dark cloud". The Nimbus racing brooms may also take their name from two racehorses, one of which won the Epsom Derby in 1949 (Wikipedia). -BB
Did Harry's Nimbus 2000 belong to the school? First years, after all, weren't allowed to bring their own brooms with them to Hogwarts. An exception for Harry was made for him to join the team due to "special circumstances", but this probably means that the broom destroyed by the Whomping Willow (PA9) was a school broom. It is no wonder Harry had to look for a new broom (PA10, PA12) to buy when his Nimbus was destroyed, as there was no way he could have played Quidditch on a old, slow school broom.
Lexicon list of Broom Manufacturers