The Three Jewels

Also called the Three Treasures, the Three Refuges, or the Triple Gem, these are, most simply put, what Buddhists take refuge in and look to for guidance. The Three Jewels are the Buddha, the Dharma, and the Sangha.

Each of these words has a variety of meanings, but the basic definitions are:
The Buddha: The historical or Shakyamuni Buddha (although this can also mean a being who has fully realized their Buddha-nature, who is enlightened)
The Dharma: The teachings of the Buddha, which includes knowing them and acting upon them with appropriate behavior.
The Sangha: 'The community', which can refer to monks and nuns, all enlightened beings, and all practicing Buddhists.

Not only do Buddhists look to the Three Jewels for guidance, but they may also 'take refuge' in them.

Here is a simple way in which a Buddhist may take refuge, which is the way of Theravada Buddhists:
I go for refuge in the Buddha.
I go for refuge in the Dharma.
I go for refuge in the Sangha.
(also in the Pali language)

For more common refuge vows, please see this post about taking refuge. Also, please see my post 'How do I become a Buddhist?'

May all beings be happy!