A deferred sentence is a sort of temporary sentence in legal terms. The situation arises when a defendant is given a period of probation which must be completed, during which the sentence is counted as deferred. The outcome of the situation depends on the defendant's ability to fulfill the probation terms, and depending on that they're either cleared of their charges or required to serve the sentence's full terms. It should be noted that a deferred sentence isn't always available to defendants, as they need to admit to the crime in question in order to be given one - that is, a defendant is obliged to plead guilty in order to be given a deferred sentence.
If the defendant manages to successfully complete their probation without violating it in any way, the judge will dismiss the case and clear it from the defendant's criminal record - this is important, as it gives the defendant the right to claim that they've not been charged with the crime in question and doesn't leave a mark on their criminal record (as opposed to some other types of pending sentences). Violating one's probation leads to the requirement that the sentence terms are completed in full, active immediately after the probation has been violated.
Deferred sentences are commonly given to first-time offenders and are somewhat rare beyond that - committing a second offense usually prohibits one from receiving a deferred sentence, as does committing a first offense which is of a relatively more serious degree.