Orb

An Orb is a ball of blue or white light, which accompanies the user in many forms, most commonly in a teleportation method, Orbing. While Whitelighters and Elders have the common blue white orbs, Darklighters have black and purple orbs which resembles them being evil. Another type of orb is a white, and golden or red orb, used by Witches when summoning a ghost, teleporting with a spell and glamouring their appearance. Witches orb are also the most common teleport method of ghosts.

In the episode The Last Temptation of Christy, Simon Marks is shown to have a different type of orbing, most likely an effect combination of Orbing and Whirling. Also, The Elders have a slightly different effect of orbing from Whitelighters, and even some of them, different color of orbs. (such as Gideon).

Orb Control
The ability to ultilize orbs for various magical purposes:

Photokinesis
The power to create and manipulate light, is used by Whitelighters, with an orb-like effect. Leo demonstrated this ability in Just Harried and Witchstock. Paige, Wyatt and Chris also possess this ability.

Hovering


When Whitelighters or Elders meditate, they hover and "sit" on orbs. This power has been demonstrated by Ramus, an Elder, in Witches in Tights, Leo in Size Matters, and Paige in The Jung and the Restless and Gone with the Witches. However, when Whitelighters merely hover, they do not display orbs (Witch Way Now). This meditative style of hovering has been displayed by Leo Wyatt, Ramus, Paige Matthews and Melinda Halliwell.

Trivia

 * Dead witches like Patty have written entries in the Book of Shadows from the afterlife, on-screen and off-screen, with a single witch orb as a pencil.