There are two ways for a married woman to leave her marriage: upon the death of her husband or upon receipt of a get. Lacking either one of these, she is still married. Were she to remarry, halakha would not recognize it. Occasionally, a husband disappears, and it is not clear whether he is alive or dead. This leaves his wife an aguna (chained wife). In such a tragic case, extreme efforts are made to clarify his status. If it can be proved he is dead, she is free to remarry.
