It essentially means something is boring, overused, and predictable.
Here are some synonyms for banal:
* Commonplace
* Clichéd
* Hackneyed
* Insipid
* Mundane
* Ordinary
* Trivial
* Uninteresting
Here are some examples of how "banal" can be used:
* "The movie's plot was so banal, I could predict the ending from the first scene."
* "Her conversation was filled with banal observations about the weather and traffic."
* "The artist's work was criticized for being too banal and uninspired."