In the early 1850s when San Francisco began its battle against the United States to gain title to its PUEBLO LANDS, the land in dispute was referred to as the Pueblo Lands.
This was everything outside of the city's 1851 charter line, specifically Divisadero Street on the west and approximately 26th Street on the south. The northern and eastern boundaries were, of course, the bay. The battle became known as the Pueblo Lands case.
By the early 1860s, however, the term OUTSIDE LANDS began to appear in the newspapers, referring to everything OUTSIDE of the city limits, which were the INSIDE lands. Large areas outside of the city's boundaries (and within the Pueblo or Outside Lands) already had commonly accepted names: the Mission, the Potrero, as well as the large ranchos: San Miguel, Bernal, Laguna de la Merced.
It seemed that the only area outside of the city's boundaries which didn't already have a commonly-used name was the area west of Twin Peaks. By default, the OUTSIDE LANDS came to be the designation of a small part of the PUEBLO LANDS/OUTSIDE LANDS.
The Alta of December 12, 1865 reported "THE OUTSIDE LANDS--The decision of Judge Field, in the US Circuit Court, confirming the claim of San Francisco to 17,000 acres (actually 17,775 acres) of pueblo land is generally regarded by the lawyers as final. The area of 17,000 acres is about 26 square miles (actually 27 square miles)."
Don't be fooled by the area. That referred to public lands, not to the large, privately owned ranchos which accounted for additional square acres and miles.
So, to be historically accurate, Outside Lands (Wikipedia notwithstanding) refers to everything west of Divisadero Street and south of 26th Street.