Largely U.S. legal jargon that refers to a very fast U.S. Federal District Court. (A docket is a court’s schedule or timetable.) The life of cases in the United States Federal Courts can vary dramatically, slow courts typically taking three to five years to complete a case through trial (though there are even odd notorious cases that have been pending for more than a decade.) However in principle, a case in for example the United States District Court could be completed in months, if every deadline available in the Federal Rules of Civil Procedure were strictly adhered to (in practice this is rarely feasible.)
Fast courts typically take a little over a year, but a few districts, notably the Eastern District of Texas (until recently) and the Eastern District of Virginia, typically hear cases within seven to nine months, have very tight scheduling rules, and rarely allow any delay by defendants or entertain motions for an extension of time. However, as a court’s reputation as rocket-dockets attracts a larger case-burden, their speed can decline markedly.
However, some dockets are also favored for other reasons including an occasional reputation for pro-local or anti-foreigner chauvinism, or even antipathy towards certain nationalities; their judges, sensitive to such concerns, increasingly aggressively counter efforts to exploit any such biases.
Because of the fixed, fast timetable that the United States International Trade Commission runs §337 investigations on, it is also sometimes seen as a rocket docket. See Forum Shopping.