Most commonly refers to the area around the bay located in the northern region of California. The peninsula part is based around San Francisco. The other major areas include Oakland in the east bay, and San Jose in the south bay. The Bay Area constitutes of all those regions and suburbs of those cities near the bay. There are, however, common misconceptions of the bay area, such as the Bay Area of Memphis, Tennessee, as well as a few others. THE BAY AREA MOST COMMONLY REFERS TO THE REGION IN NORTHERN CALIFORNIA, YOU CAN NOT DENY THAT.
The rapper Lil' Wyte states that he is from the Bay Area. He is not from the Bay Area in Northern California, so he is in fact a pussy bitch. E-40 and Too Short are from the Bay Area; Vallejo and Oakland, respectively. Dont hate on the Cali Bay Area just cause your state's Bay Area isnt as well known.
Here's an analogy...When people say Portland (there are 14 Portlands in the U.S.), they're most likely talkin about the one in Oregon.
(my bad if i didnt name your city in the definition of the bay area...i got love for the whole bay...vallejo, concord, richmond, pittsburg, sunnyvale, palo alto (EPA), fremont, mateo, marin, berkeley, and every lil town i forgot from gilroy to sactown to santa rosa and back down)