A “triple-double” in basketball is when a player has double digit totals in three of five statistical categories—points, rebounds, assists, steals and blocked shots. The usual combination is points, rebounds and assists because ten or more steals or blocked shots in a game is rare. The National Basketball Association first recorded the"triple double” for the 1979-80 season. “Those 12 assists for (Magic—ed.) Johnson were part of his third triple double (double figures in points, rebounds and assists) of the young season” was cited in print in November 1980.
 
There is some debate as to what person coined the name “triple-double.” Los Angeles Lakers public relations director Bruce Jolesch took credit for it, when he attempted to record the outstanding play of Magic Johnson. Harvey Pollack, the Philadelphia 76ers’  director of statistical information, also claimed to have coined “triple-double.”
 
   
Wikipedia: Double (basketball)
Triple-double
A triple-double is defined as a performance in which a player accumulates a double digit number total in three of five statistical categories—points, rebounds, assists, steals, and blocked shots—in a game. The most common way for a player to achieve a triple-double is with points, rebounds, and assists, though on occasion players may record 10 or more steals or blocked shots in a game. The origin of the term “triple-double” is unclear. Some sources claim that it was coined by former Los Angeles Lakers public relations director Bruce Jolesch in the 1980s in order to showcase Magic Johnson’s versatility, while others claim that it was coined by then Philadelphia 76ers media relations director Harvey Pollack in 1980. The triple-double became an officially recorded statistic during the 1979–80 season.
 
A triple-double is seen as an indication of an excellent all-around individual performance.
 
5 November 1980, The Register (Santa Ana, CA), “Lakers hang on to beat Trail Blazers” by Steve Springer, pg. E1, col. 1:
Those 12 assists for (Magic—ed.) Johnson were part of his third triple double (double figures in points, rebounds and assists) of the young season.
 
11 March 1981, The Register (Santa Ana, CA), “Magic leads Lakers past San Antonio” by Steve Springer, pg. E1, col. 5:
Not only were his (Magic Johnson’s—ed.) statistics back (it was his fourth triple-double of the season), but so was that smile, and the enthusiasm.
 
12 January 1982, Greensboro (NC) Record,  “Nets watch Bird ring up a rare ‘triple-double’” (AP), pg. B4, col. 4:
As usual, Boston’s No. 1 hustler Monday night was Larry Bird, who put together a rare “triple-double,” reaching double figures in points, rebounds and assists. He scored 25 points, pulled down 14 rebounds and passed for 10 assists in 44 minutes.
   
Los Angeles (CA) Times
They’re Vintage Triple-Doubles
April 20, 2002|J.A. Adande
Forty years ago, Oscar Robertson put together a season unique in NBA history.
 
You want numbers? Peep the Big O’s stats from 1961-62: 30.8 points, 12.5 rebounds, 11.4 assists a game.
 
That’s right, he averaged a triple-double.
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The term “triple-double” was coined by Bruce Jolesch, the former Laker public relations director who needed a way to summarize Johnson’s penchant for recording double figures in points, rebounds and assists.
   
USA Today
Philly’s Pollack has kept track of NBA from the start
Posted 4/18/2008 4:51 PM
By Dan Gelston, AP Sports Writer
PHILADELPHIA — Harvey Pollack has a dedication to numbers that would make a numerologist jealous. Add in a love for oddball NBA statistics that only he can break down and it’s no wonder he’s been called “Super Stat” for more than 40 years.
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Erving’s arrival in Philadelphia started Pollack’s fascination with dunk stats, and Magic Johnson’s amazing games made Pollack realize he needed a catchy title for double digits in points, rebounds and assists.
 
The triple-double was born.