(Or "linear assignment") Any problem involving minimising the sum of C(a, b) over a set P of pairs (a, b) where a is an element of some set A and b is an element of set B, and C is some function, under constraints such as "each element of A must appear exactly once in P" or similarly for B, or both.
For example, the a's could be workers and the b's projects.
The problem is "linear" because the "cost function" C() depends only on the particular pairing (a, b) and is independent of all other pairings.
http://forum.swarthmore.edu/epigone/comp.soft-sys.matlab/bringhyclu. http://soci.swt.edu/capps/prob.htm. http://mat.gsia.cmu.edu/GROUP95/0577.html. http://informs.org/Conf/WA96/TALKS/SB24.3.html.