In literature, a motif is any recurring element that has symbolic significance. For example, it could be a thing, a place, or a statement. The green light in The Great Gatsby is a motif, as is the repeated statement, "My father said that the reason for living is getting ready to stay dead." in William Faulkner's As I Lay Dying.
In music, a motif is a perceivable or salient recurring figure or fragment that may be used to construct the entirety or parts of complete melodies, themes, and even accompaniments.
In biochemistry, a motif is a recurring pattern in the sequence of nucleotides or amino acids — see sequence motif.