A divergence between the price behavior of a position or a portfolio and the price behavior of a benchmark. This is often in the context of a hedge or mutual fund that did not work as effectively as intended, creating an unexpected profit or loss instead.
Tracking errors are reported as a "standard deviation percentage" difference. This measure reports the difference between the return an investor receives and that of the benchmark he or she was attempting to imitate.
Investment dictionary. Academic. 2012.