A player's regular issue card from an officially licenced brand issued in the first year the player is eligible to appear on a trading card.

The Beckett Definition of RookieCard -- which is the one most widely accepted by The Hobby -- states that a rookiecard cannot be a subset card, insert card or (in most cases) RedemptionCards. It MUST be a regular base set card.

If a player has more than one base set card in the same set, then the rookiecard tag is given to the regular card (assuming that the other card is from a special subset). If a player has more than one base set card in the same set, but the two cards are produced in different quantities (i.e. one is short-printed and the other is not), then the more common card is given the rookiecard label. Also, just because a card may say something like "Prospect," "Rated Rookie," or "Star Rookie" on it doesn't necessarily mean it's a rookie card. Conversely, if a card does not say "Rookie" on it somewhere, it may still be his rookie card.

Many of the cards produced by Classic (and other so-called "draft pick" sets) are not considered rookie cards, because they are not licensed by the respective leagues and teams. This is why many of the players in such sets are still pictured in their college and high school uniforms. However, a player need not be pictured in a major league uniform for a card to be considered a rookie. For example, MannyRamirez is shown wearing street clothes on his 1992 Bowman rookie card. Since Ramirez had signed a professional contract, and because the 1992 Bowman set was officially licensed by Major League Baseball and the Player's Association, this is considered one of his rookie cards.

In recent years with the trend by card makers to "short-print" their base-sets (especially the rookie cards), the line between what is "base" and what is "insert" has become blurred, almost to the point of no return.

More details here: HockeyRookieCards, BaseballRookieCards