ATP Masters 1000 tournaments
The ATP Masters 1000 tournaments, also known as Masters 1000 or ATP 1000 events, are an annual series of nine tennis tournaments featuring the top-ranked players on the ATP Tour since its inception in 1990. The ATP 1000 tournaments, sitting below the Grand Slam tournaments and the year-end championships, make up the most coveted trophies on the annual ATP Tour calendar.
Source: Wikipedia — ATP Masters 1000 tournaments (CC BY-SA 4.0)