This page contains information regarding Star Trek: Discovery, and thus may contain spoilers.
A career was a profession for which an individual trained and followed as a calling in life. During their work life, the individual was given the opportunities for advancement and for gaining greater responsibilities.
Commander William T. Riker studied the career of Ambassador Sarek in school, which included the treaty of Alpha Cygnus IX, the Coridan admission to the Federation, and the Klingon Alliance. Sarek himself had studied the career of Jean-Luc Picard and deemed it "satisfactory," something which Picard considered high praise from a Vulcan. (TNG: "Sarek")
In 3189, Commander D. Nhan gave up her Starfleet career to stay aboard the USS Tikhov. For her, as a Barzan, it was important to deliver the family of Doctor Attis, who had died from exposure to a coronal mass ejection, to Barzan II for burial and to successfully complete the first Barzan watch over the Tikhov's seed vault. (DIS: "Die Trying")