Alumni refers to a group of graduates.

I subscribe to this fun, daily newsletter called theSkimm (endorsement: it's awesome, you should sign up for it at theSkimm.com). In addition to sending you the top headlines and a brief paragraph outlining the important details, they started adding in a section at the bottom called 'Thing to Know.'

About two weeks after I graduated, theSkimm provided the answer to the question that had been gnawing at my brain for weeks:

I am an alumna, my brother is an alumnus, all of my girlfriends are alumnae, and my graduating class are alumni. I changed my Twitter bio (which previously stated I was an alum... still accurate!) right after I read this.

Too bad I never learned this in college!