CA


 * calcium: a white metallic element that burns with a brilliant light; the fifth most abundant element in the earth's crust; an important component of most plants and animals


 * ca.: The Latin word circa, literally meaning about, is often used to describe various dates (often birth and death dates) that are uncertain.


 * .ca is the Internet country code top-level domain (ccTLD) for Canada.


 * Certificate Authority. An authority trusted and authorised to issue and revoke Digital Certificates. The Certificate Authority is also responsible for maintaining the Certificate Revocation List.