A tutor is card that allows a player to search for a card in his/her deck. Most tutors search for a specific type of card, but some can search for any card. Tutors are often balanced by having a heavy upfront cost (e.g. Hostage is a Double that tutors for Connections); by requiring the player to reveal the tutored card, often to prove that the found card is indeed of the proper type (e.g. Fast Track tutors for Agendas, but the found agenda must be revealed to now be in HQ); or by having some kind of additional condition for the tutored card (e.g. Test Run tutors for Programs but then returns them to the top of the deck at the end of the turn). Tutors always also shuffle the player's deck after finding the card.
Tutor can also be a verb, as the act of using a tutor is referred to as tutoring.
The term tutor originates from the very first CCG card with this effect: 'Demonic Tutor' from the first release of Magic: The Gathering in 1993.