Broad is a colloquial term for woman which originated during the 1930s.
There is some disagreement about the origin of the word. Many believe the term refers to the shape of women's hips, arguably their most defining characteristic, which are usually broader than the hips of men. Others say that it comes from the American-English word "abroadwife" which meant slave woman or a woman who was separated from her husband. Another suggestion is that it comes from a slang word for "ticket" common in the 1910s. Around this time prostitutes may have been called broads as they were a pimp's "meal ticket." The word broad was later used to define any woman of questionable virtue.
The term broad is outdated by modern standards, but is still used in some social circles including by Italian-Americans in Philadelphia, South and North Jersey, and New York City.