A ‘Triple-Double’ is recorded when a player records 10 or more in three of the following categories: points, assists, rebounds, steals, and blocked shots. Prior to the 1973-74 season, the NBA did not record steals and blocked shots.
An amazing stat involving NBA Triple Doubles is that in 1961-62, Oscar Robertson while playing for the Cincinnati Royals averaged a triple-double over the entire season. He averaged 30.8 points, 12.5 rebounds, and 11.4 assists. Robertson is the only player to ever accomplish this. During that season, he also set the mark for most triple-doubles in one season with 41 (played in 79 games). Those are two records that will probably never be broken.
Wilt Chamberlain recorded the only NBA Double-Triple-Double; 22 points, 25 rebounds, and 21 assists. Also in 1968, Chamberlain had a streak of 9 consecutive games in which he recorded a triple-double.