A trial is, in the most general sense, a test, usually a test to see whether something does or does not meet a given standard.
In law, a trial is the presentation of information in a formal setting, usually a court, with the object of determining whether or not a person (or entity, such as a corporation) has broken a law. See, e.g., jury trial
In science, a trial is the result of a given run of a given experiment, with the usual object of testing a scientific hypothesis. Multiple trials are usually run, when possible, for an experiment, in order to offset the effects of random error.
In probability, a trial is an action that results in one of a number of outcomes or elementary events.
In Motorcycle racing, trail is a kind of competition.
See also: trial and error