The title of Tennessee Williams' play A Streetcar Named Desire refers to a few different things.
While the title most poignantly refers to the actual streetcar Blanche takes to get to her sister's, the title also refers to the journey one takes in life.
Blanche's journey begins as she climbs onto Desire. Blanche's desire to escape her past, and the loss of Belle Reve, forces her to come to her sister's in New Orleans. Her past as a prostitute has followed her--her sexual desire openly evident as she takes every measure to flaunt herself (remember her silhouetted figure against the sheet).
Blanche's journey through life has been one led by her desire. her first love was triggered by her need to be loved and taken care of. Blanche lost her teaching position because of her desire for a student. Her sexual nature leads to her rape. Her relationship with Mitch is began because of his need for a woman unlike his mother. Desire essentially rules the play-- much like it runs the streets of New Orleans.