Just as Los Angeles has two Eastsides (one being the largely Latino enclave east of the LA River and the other being South Los Angeles east of the 110 and/or Main St) it also has two Westsides. One Westside is a collection of LA's westernmost neighborhoods (such as Bel Air, Brentwood and Venice) and the area's enclosed cities (like Culver City, Santa Monica and Beverly Hills).
The other Westside is the area of South Los Angeles (and the surrounding communities) that lie west of the 110, south of the 10 and east and north of the 405 (although some of those are can make the historical argument for being part of the South Bay, despite being separated from the Santa Monica Bay by miles of land and other cities). This westside, after white flight in the 1950s to the present, is also colloquially known as "The Black Westside" and indeed, it's still, as of 2011, home to most of Los Angeles's black residents and businesses despite changing demographics.
The region of South LA's Westside is a large area bounded by South LA's Eastside to the east, The Harbor to the southeast, The South Bay to the west and south west, The Westside to the northwest and Midtown to the north. Definitions differ of exactly what communities constitute the region with several also claiming the South Bay and/or The Harbor. No doubt part of the reason these neighborhoods are in question are due to residents of and developers in those communities eager to disassociate themselves with South LA, which carries negative connotations for many.