A rookie was a newcomer playing their first year of a sport.
The Human baseball player Willie Mays's rookie year was 1951. (DS9: "In the Cards") Buck Bokai's rookie year was 2015. (DS9: "Past Tense, Part II")
A baseball card that featured a player in his rookie year was called a rookie card. (DS9: "In the Cards")
According to Star Trek: Deep Space Nine Companion, p. 343, the character of Ekoria from "The Quickening" was originally named "Ekorio", which was an anagram of the word "rookie".