In American and Canadian television, a mid-season replacement is a television series that premieres in the second half of the traditional television season, usually between January and May.
 Mid-season replacements usually take place after a show that was in the fall schedule was canceled or put on hiatus, outside factors such as an actor's family emergency or personal illness led to a delay in the program's debut, a program was purposefully scheduled for mid-season (for example, shows NBC airs on Sunday nights after the NFL season ends, as it only takes up the first half of the television season), or a program had a shortened season for some other reason which resulted in a time slot that needed filling.
 A few shows in American television history have been perennial mid-season replacements; "American Idol", for example, from its second season onward, aired from January to May each year, to great ratings success.
The first season of Happy Endings, an American television series, premiered on April 13, 2011 and concluded on August 24 of the same year.
 ABC officially picked up the show on May 18, 2010, where it premiered on April as a mid-season replacement,
The first season of the television series Buffy the Vampire Slayer premiered on March 10, 1997 as a mid-season replacement on The WB and concluded its 12-episode season on June 2, 1997.
 The first season aired on Mondays at 9:00 pm ET.
"Undercover Boss" is an American 2010 reality television series, based on the British series of the same name.
 The first episode of the first season premiered on February 7, 2010, after Super Bowl XLIV, and featured Bob O'Donnell, President and Chief Operating Officer of Waste Management, Inc.
 On March 9, 2010, CBS announced it had renewed "Undercover Boss" for a second season.
 On July 28, 2010, CBS announced four company executives had signed up for the second season of "Undercover Boss", the executives are from NASCAR, DirecTV, Chiquita Brands International and Great Wolf Lodge, Inc. The Choice Hotels CEO, Steve Joyce, was the first boss for the second season of the show on September 26, 2010.
 On March 27, 2011, CBS officially renewed "Undercover Boss" for a third season.
 On May 18, 2011, CBS then announced that it would be holding the show for a mid-season replacement to premiere Sunday January 15, 2012, with an undetermined amount of episodes.
 The third season premiered on January 15, 2012.
 The fourth season premiered on November 2, 2012.
 The fifth season premiered on September 27, 2013.
 The sixth season premiered on December 14, 2014.
 The eighth season premiered on December 21, 2016.
Undateable is an American television sitcom that aired on NBC from May 29, 2014 to January 29, 2016 and originally premiered as a mid-season replacement.
 The series was created by Adam Sztykiel and is based on the book "Undateable: 311 Things Guys do That Guarantee They Won't be Dating or Having Sex" by Ellen Rakieten and Anne Coyle.
 On May 8, 2015, NBC renewed "Undateable" for a third season that consisted entirely of live episodes, which premiered on October 9, 2015.
 On May 13, 2016, NBC canceled the series after three seasons.
"The Unit" is an American drama television series.
 It began airing on CBS on March 7, 2006, in the United States, as a mid-season replacement.
 Created by David Mamet, "The Unit" follows a United States Army top-secret special forces team and their missions abroad, in addition to the effect their careers have on their wives and girlfriends.
 "The Unit" began its first season on March 7, 2006 and concluded on May 16, 2006; the second season debuted on September 19, 2006 and completed on May 8, 2007.
 The third season started on September 25, 2007, with a hiatus occurring after the 11th episode due to 2007–2008 Writers Guild of America strike.
 The show was picked up for a fourth season by CBS on May 12, 2008.
 The fourth season began on September 28, 2008 and ended on May 10, 2009, which was also the series finale as the show was not renewed for a fifth season.
 A total of 69 episodes of the series aired.
The first season of the American television medical drama Grey's Anatomy, began airing in the United States on the American Broadcasting Company (ABC) on March 27, 2005, and concluded on May 22, 2005.
 The first season introduces the main character, Meredith Grey, as she enrolls in Seattle Grace Hospital's internship program and faces unexpected challenges and surprises.
 Season one had nine series regulars, four of whom have been part of the main cast ever since.
 The season initially served as a mid-season replacement for the legal drama "Boston Legal", airing in the Sunday night time slot at 10:00, after "Desperate Housewives".
 Although no clip shows have been produced for this season, the events that occur are recapped in "Straight to Heart", a clip-show which aired one week before the winter holiday hiatus of the second season ended.
 The season was officially released on DVD as two-disc Region 1 box set under the title of "Grey's Anatomy: Season One" on February 14, 2006, by Buena Vista Home Entertainment.
The first season of the American television comedy series "Rules of Engagement" premiered on February 5, 2007 and concluded on March 19, 2007.
 It consists of 7 episodes, each running approximately 22 minutes in length.
 CBS broadcast the first season at 9:30 pm in the United States.
Rob (stylized in promos as ¡Rob!)
 is an American sitcom television series that premiered on CBS on January 12, 2012, at 8:30 pm (ET) as a mid-season replacement for "Rules of Engagement", and ended on March 1, 2012.
 The series stars Rob Schneider alongside Cheech Marin, Claudia Bassols, Diana Maria Riva, Eugenio Derbez, Ricky Rico, and Lupe Ontiveros.
 The show was produced by "Two and a Half Men"' s The Tannenbaum Company and CBS Television Studios.
 On May 13, 2012, CBS canceled the series.
Rules of Engagement is an American sitcom that ran on CBS from February 5, 2007, to May 20, 2013, originally airing as a mid-season replacement.

Question: The first season of which American television comedy series, premiered on CBS on February 5, 2007, originally airing as a mid-season replacement?
Answer: Rules of Engagement