Contactless refers to a family of wireless technologies that have extremely short range.
Contactless technology typically takes the form of a small chip embedded in a phone, key fob, or plastic card (like a credit card). The objet with the contactless chip is simply placed on or very near a reader device (such as a pad on a debit card terminal, kiosk machine, or turnstile) to initiate a transaction.
Despite the name "contactless", the technology has such a short range (typically 1-2 inches) that the phone or card usually must be "tapped" against the reader device for the transaction to occur reliably. However since it does not actually require contact, a contactless card can be left inside a wallet, for example, and still work.
Contactless cards are used most often for financial transactions, as a replacement for swiping a magnetic stripe card or inserting a card with an exposed "smart chip". In this way it can function as a credit card, debit card, transit pass, or any type of stored-value card.
Contactless chips can also be put into phones, where they can interact with secure apps on the phone to provide multiple services, and interactive control for greater security.
Although contactless technology is related to RFID, it is not exactly the same. RFID tags used in commercial and industrial applications can be read from several feet away; Contactless cards cannot.
The leading global standard for contactless technology is NFC.