Best ask the Olympic members, Howard - I don't know the ins and outs of it, just know it's a membership category.
The O Club is an athletic club with over 7000 members. It owns two separate facilites, the Downtown Club and the Lakeside Club. The Downtown Clubhouse is housed in a beautiful facility very near Union Square in downtown SF. The Lakeside Clubhouse is located in the Souwthwest corner of the City adjacent to Lake Merced and is the site of the three O Club golf courses (Lake, Ocean and Cliffs), the tennis courts, and a beautiful old clubhouse with dining rooms, workout rooms, locker rooms, and a small pool.
All members of the club have full privileges to use the downtown facility. All members also have full access to the Lakeside clubhouse, slightly restricted access (in terms of tee times) to the golf courses, limited guest privileges on the golf courses, and they must pay green fees whenever they play any of the courses. This base class of member is colloquially referred to as a "Downtown" member. The official name within the club is "Member Not Holding a Golf Privilege", cleverly abbreviated to MNHGP.
For a relatively substantial additional sum of money (and after sitting on a waiting list for something like 7-10 years), downtown members can become a "Member Holding a Golf Privilege", colloquially referred to as "Golf" members but officially referred to as MHGP. This class of member has unlimited access to the golf courses (preferential tee times, no blackout times), pays a fixed monthly green fee (on top of their base monthly dues) and they no longer have to pay per-round green fees. They also have significantly more liberal guest privileges.
Members can also purchase a tennis privilege for a modest sum of money and play unlimited tennis instead of a per use fee.
The only members who can bring guests out onto the Lake Course are MHGP, so if you know someone who is an "Olympic Club Member" who never invites you out to play the Lake Course, you can assume that they are probably MNHGP. MNHGP are allowed to bring one guest out on the Ocean Course every month. They have unlimited guest privileges on the 9-hole Cliffs course.
More than you might ever want to know about the O Club. : )