If you have been around San Francisco for any amount of time, you will definitely see a reference to the Golden Gate, the most obvious being the Golden Gate Bridge. You will also hear the term used in almost any song talking about San Francisco. We now have restaurants, apartment houses, businesses, hobby clubs, etc. using the name to show themselves as local and loyal to the Bay Area.
The term Golden Gate refers to the entrance of the bay between Marin and San Francisco which is now connected by the bridge. Before the bridge, the name was still used for that specific area.
Why Golden Gate? Many think it is a term relating to the California Gold Rush. It makes sense, but it is incorrect. It was actually named by John C. Fremont after he first viewed the entrance to the bay. It reminded him of the sea entrance to to Byzantium, now called Istanbul. The entrance to that historic harbor is named Chryoceras (Greek for Golden Horn). The geographical characteristics, as well as the possible commercial uses of this area, are what led Fremont to name this area of the bay Chrysopylae, or Golden Gate.
Reference: San Francisco Memoirs 1835-1851: Eyewitness accounts of the birth of a city, by Malcolm E. Barker