Professional football teams hold a “mini-camp” (or “minicamp”) during the offseason. Most mini-camps are regularly scheduled for rookies and last a weekend (three days). The term “mini-camp” has been cited in print since at least July 1970.
 
Another program that football teams hold during the offseason is the “organized team activity” (OTA).
     
 
Wikipedia: Mini-camp
A mini-camp is a short camp held by National Football League (NFL) teams usually in May of each year. The camp usually only lasts 3 days, but the length varies by a day or two depending on the head coach’s preference. Mini-camps are geared toward getting the newly drafted rookies acclimated to the NFL playing schemes. It also gives coaches and team administrators the chance to see their new players in action learning plays from their new team’s playbook. Several veteran players of each team will also attend mini-camp to refresh their skills and get acquainted with the new players coming in. Attendance requirements for mini-camp are entirely up to each individual head coach. Some head coaches push for all of the players to be there, while others ask for just the rookies and younger players to attend. The drills and plays run at camp are conducted in shorts and t-shirts or jerseys. They are not “full contact” drills.
   
(Oxford English Dictionary)
minicamp, n.
N. Amer. Sport.
A place where a particular professional sports team carries out trials of potential new players, or training for a particular set of players, prior to its main pre-season training; the sessions held at such a place.
1977 Washington Post 25 May e3/1   Forty-five players attended the opening of the three-day minicamp.
1992 Sports Illustr. 7 Sept. 112/2   Rookies have been scrutinized aplenty in minicamps.
 
24 July 1970. Anderson (IN) Herald, pg. 17, col. 2:
Mini-Camp Opened
For Card Veterans
ByYJAMES F. WIECK
ST. LOUIS (UPI)—A mini-camp for St. Louis Cardinal Football Veterans opened here Thursday.
 
28 July 1970, Ogden (UT) Standard-Examiner, pg. 4B, col. 1 photo caption:
A GROUP OF YOUNGSTERS watch St Louis Cardinals running back Johnny Roland try to twist him self into shape at a mini-camp for veteran players.
 
17 April 1971, The Times-Picayune (New Orleans, LA), “Saturday’s Heroes” by Nate Cohen, sec. 3, pg. 1, col. 1:
“I wish I had signed with Baltimore now,” Granger jokingly recalled in between Sain “mini-camp” sessions Friday on David Dr.
 
11 May 1971, Dallas (TX) Morning News, “From Other Rooms” by Bob St. John, pg. 2B, col. 5:
During George Allen’s mini camp in Washington, Sonny Jurgenson answered an assertion by former coach Bill Austin that he could not pass more than 40 yards due to a chronic throwing arm that was operated on in 1968.
 
1 July 1972, The Times-Picayune (New Orleans, LA), “Sants End Mini-Camp” by Bob Stalder, sec. 3, pg. 1, col. 8:
The Saints completed what head coach J. D. Roberts termed “a real good camp” with the final workouts of their pre-Hattiesburg training camp Friday.
 
14 Apri 1976, The Plain Dealer (Cleveland, OH), “Saints sign Muncie to 7-year contract” (AP), pg. 3-F, col. 2:
The Saints excused him from a minicamp practice Tuesday so he could get a little sleep and look around.
 
Google News Archive
28 May 1976, The Daily Sentinel (Middleport-Pomeroy, OH), pg. 12, col. 3:
MIAMI (UPI)—Miami Dolphins Coach Don Shula scheduled five practices for a three-day “mini camp” opening today to get a close look at 27 of his younger football players.
 
NY Giants
Posted:May 11, 2013
Rookie Mini-Camp Wrap-Up Report
John Schmeelk and Paul Dottino recap Giants Rookie Mini-Camp
 
Midway Illustrated (Chicago Bears)
Chicago Bears Rookie Mini-Camp Report: Jon Bostic is Fast, But Is He Physical Enough?
Written by Brett Solesky on Sunday, 19 May 2013 19:17.