The three jewels, or triple gem, are the Buddha, his teaching and the community. Taking refuge in them is the act by which one becomes a Buddhist, recited in a simple formula across all Buddhist traditions. They are called jewels because they are rare and precious, and refuges because they protect from suffering.
Three Jewels
The Buddha, the Dhamma and the Saṅgha, in which Buddhists take refuge.
Also: Triple Gem, triratna, refuge