The Disney MagicBand is a wrist band with a chip carrying a unique identifier and a radio which sends and receives RF signals. Disney combines the band with guests fingerprint (and PIN for some things) as positive identification of a guest. The bands allow people to sign up for front-of-the-line access at a specific time for major attractions or characters. This increases their enjoyment of the park, a benefit to the guest, and increase the opportunity that they may spend more on concessions or vendors.”]
Source: https://www.csoonline.com/article/2867326/the-magic-of-disney-magicbands.html