Force stealth

"You blend in with the universe. Think of it as Force camouflage. The trick is to become so comfortable with it that you can slip into this state of being… dissolved, yet still carry on functioning, fully aware."

- Jacen Solo

Force stealth also referred to as Force Concealment or Buried Presence was a power that was used by highly skilled Force-sensitives to mask their Force alignment (Light or Dark), their ability to use the Force, or even their entire presence from other Force-sensitives.

Effects
This ability manifested in different forms; Vergere would shrink her presence in the Force to a microscopic size, where she was almost undetectable and able to avoid mental attacks, even from Luke Skywalker. Darth Sidious was the most powerful and notorious user of this power, having hid his dark nature for over three decades from the Jedi Council, even when in the same room. It has been argued that Revan may have used the technique to shield his true light side affiliation on Korriban in order to infiltrate the Sith academy. Darth Traya used a powerful version of this to evade both the surviving Jedi and her Sith apprentices, as well as mask her nature from her own student, Meetra Surik who in turn may have mastered this ability. Other users included the Jensaarai, who constantly hid their presence in the Force from both the Sith under Darth Vader and the New Jedi Order.

Xanatos used this kind of power to shield his presence when he infiltrated the Jedi Temple.

Jedi Masters Obi-Wan Kenobi and Yoda both used a form of Force concealment to shield themselves from Darths Sidious and Vader in their exile.

One of the more prevalent derivatives of Force Concealment was the Quey'tek meditation. When properly applied and maintained, a Sith Lord or Dark Jedi could mask their own dark signatures appearing completely benevolent to even the most powerful and alert Jedi.

Known users of the Quey'tek meditation included Asajj Ventress, Dooku (although Obi-Wan Kenobi and Anakin Skywalker were eventually able to see through his shielding) , and possibly Darth Maul and Darth Zannah. Anakin's grandson, Jacen Solo, also used this technique to hide Lumiya's dark presence. Jacen also used it to hide his own emotions from other Force-users whenever he was upset or under stress. Ben Skywalker later gained this power from Jacen and likewise his mother Mara Jade Skywalker learned it from him. Luke Skywalker used this ability to sneak up on Jacen during the Battle of Kashyyyk. Luke's control of this Force ability was so precise he was able to allow certain individuals including his own son to sense his presence when hiding from adversaries. By the time Jacen became Darth Caedus, he had used the power so much that he was able to constantly remain hidden with little effort, and taught the power to his apprentice, Tahiri Veila.

The Hidden Ones of the Baran Do sages used this power to fake their own deaths during their farewell ceremony. The Agents of Ossus were adept at using this power to evade the Inquisitorius and other Imperial Force-hunters during the Dark Times.

Behind the scenes
In the Wizards of the Coast Star Wars Roleplaying Game, this ability is referred to as "Force Stealth". The original version allowed a Force-user to not only hide his or her Force sensitivity, but increase his or her ability to hide. The Revised version only provides a way to cloak one's connection to the Force, and any use of the Force causes this ability to fail, although Jedi Sentinels can learn to use Force Stealth and Force Camouflage together. The Saga Edition splits the ability into a number of distinct powers and talents.

Source

 * The Force Unleashed Campaign Guide
 * Book of Sith: Secrets from the Dark Side
 * Book of Sith: Secrets from the Dark Side