The phrase "first anniversary" refers to the one-year mark since a special event or occasion, such as a wedding, the start of a job, or the beginning of a relationship. Full definition
The announcement comes as part of the company's celebration of first anniversary of its operations in the Indian market. (techpp.com)
It would be such an awesome first anniversary present for my wonderful new daughter - in - law and awesome if you came on over to redo their kitchen. (theletteredcottage.net)
Museum Celebrates First Anniversary of PRIMED Expansion with March 23 Volunteer Appreciation Party (ashevilleart.org)