Fate is a concept of the inevitability of the future. It is linked with the concept of time, and the idea of fate is that events on a time line follow a predetermined sequence based on unalterable cause-and-effect relations. What happened, had to happen; what will happen, will happen, and when events are said to have been fated to happen. The term is somewhat synonymous with destiny, although destiny is a more limited term which describes the process of fate, starting with the present, and working forward to the future. For example, it's one's destiny to die (since all humans will die). But fate, in contrast, can be thought of as pre-determined events in the past as well as the future; for example, one can say that it was fated to be here, right now, in this present moment, and mean that it was impossible for this moment to have happened any differently. In one sense, fate is the opposite of the concept of free will, which suggests that events are not pre-determined, but that humans can alter the future by acting.
The concept of fate has figured prominently in literature. In Oedipus Rex by Sophocles, the hero Oedipus was fated to kill his father and marry his mother; accordingly, various actions are taken by different characters in the story to try to avoid this pre-determined future, but as it turns out, these actions have the opposite effect of causing Oedipus, indeed, to kill his father and marry his mother. The idea of the play is that fate is unavoidable, but literary scholars have noticed the conundrum within the Greek tragedy, which is how the concepts of fate and free will are intertwined. Characters who exercise their free will to try to avoid their fate have the grave misfortune of causing the negative result that they're trying to avoid.
A story by W. Somerset Maugham in 1933 illustrates the idea of the unavoidability of fate:
The speaker is a character called Death in The Appointment in Samarra: