C.H.U.G. (Classics, Henkei, Universe & Generations) is a fan-created term encompassing the following collector-aimed nostalgia toylines:

Classics (2006 through 2007)
Universe 2.0 (2008 through 2010)
Reveal the Shield (2010 through 2011)
Generations (2010 through 2012)
Generations: Fall of Cybertron (2012 through 2013)
Generations: Thrilling 30 (2014)
Generations Selects (since 2019)

It also includes several concurrent toylines by Takara:

Henkei! Henkei! (2008 through 2010)
United (2010 through 2011)