DigiDestined is a term unique to the Digimon media franchise. It is used in several Digimon anime and manga series. DigiDestined is an English term; in Japanese DigiDestined are known as Chosen Children. The DigiDestined (and Digidestined-like groups) are the protagonists of the Digimon franchise.
DigiDestined are children selected by benevolent beings to protect the Digital World (and sometimes Earth) from evil forces. The Digital World is a plane on which Digimon, anthropomorphic creatures that originated from data produced by Earth’s communication networks, live. The Digital World is volatile and is vulnerable to attack, and the Digimon that live there often find that they cannot defend their world on their own. Therefore, human children are recruited to defeat their enemies.
In Digimon Adventure and Digimon Adventure 02, a DigiDestined is defined by the possession of a Digivice and a link to a Digimon partner. When a Digimon is partnered to a DigiDestined that child becomes its sole source of Digivolution. Digimon become stronger through Digivolution; this is usually a difficult process to achieve but a DigiDestined's Digivice amplifies a Digimon’s power to the point where it can Digivolve easily.
Non-DigiDestined can have Digimon partners as well, but they cannot be called DigiDestined if they don't have some sort of Digivice.