noun

• A municipality of Albay, Philippines.
• A surname from Norwegian.
• Initialism of oral allergy syndrome. [A food allergy consisting of a cluster of allergic reactions in the mouth and throat in response to eating certain fruits, nuts, and vegetables.]
• Initialism of original antigenic sin. [(immunology) The propensity of the immune system to preferentially use immunological memory based on a previous infection when a second, slightly different version of the foreign pathogen is encountered, leaving the immune system "trapped" by the first response it has made to each antigen, and unable to mount potentially more effective responses during subsequent infections.]
• Initialism of Organization of American States.
• (Canada) Initialism of Old Age Security.
• (computing) Initialism of OpenAPI Specification. (a specification for machine-readable interface files for describing, producing, consuming, and visualizing RESTful Web services)
• Initialism of Organisation de l’Armée Secrète, a French organization.