<p><em>Taken from Wikipedia, the free encyclopedia:</em></p>

<p>Backtracking is a strategy for finding solutions to
constraint satisfaction problems. These are problems
with a complete solution, whereby the order of elements
does not matter. The problems consist of a set of variables
each of which must be assigned a value, subject to the
particular constraints of the problem.</p>

<p>Backtracking attempts to try all the combinations in
order to obtain a solution. Its strength is that many
implementations avoid trying many partial combinations,
thus speeding up the running-time. The term "backtrack"
was coined by the American Mathematician D. H. Lehmer
in the 1950s.</p>