Kaiser Permanente is an HMO based in Oakland. People you meet in Oakland might also say "Kaiser" to refer to the health coverage they receive through Kaiser Permanente (as in "I got my Kaiser"), or to the Kaiser Permanente Oakland Medical Center (as in "I had to go to Kaiser to see a doctor because they make you go to their doctors").
Kaiser Permanente was founded in 1945 by Henry J. Kaiser (who recognized that healthy workers are more profitable than sick ones) and their HQ is in the Ordway Building by Lake Merritt.
Wikipedia has a lot of information about Kaiser.
Kaiser was the recipient of the Legacy Award at the 2014 East Bay Innovation Awards.