Force cloak, which is also called Force camouflage or Force invisibility, was a rare Force skill that involved changing light and sound waves so that the person using it was almost impossible to see. Before the Galactic Empire took over and the Jedi Temple on Coruscant was destroyed, mostly members of the Jedi Order knew about this ability. Even though the Jedi lost a lot of their knowledge, the Disciples of Twilight, a strange group based on the Outer Rim moon of Dyspeth, became experts at using the Force to hide themselves. Another way to use it was to change how people around the Force user saw things, so they didn't notice the person sneaking around.
It's important not to mix up Force cloak with the natural ability of a Force Blank, which made a void in the Force. The first one was usually a skill that people who used the light side of the Force learned, but the second one was a natural power that only beings who were naturally drawn to the dark side had.
Force-sensitive people have been using the skill of hiding themselves in the Force since the early days of the Galactic Republic. This rare ability allowed a Force-user to use their control over the Force to bend light and sound around themselves, making it impossible to see or hear them. This skill is often a natural talent, as it's very hard to learn otherwise, which is why it's not seen very often. While it works very well when done right, keeping up the cloak took a lot of energy, and the focus needed to keep it going could make it not worth using.
Like with all Force abilities, there wasn't just one way to hide oneself. Another way, which didn't involve controlling light and sound, was a more advanced version of a mind trick or Force persuasion. This way, the user changed the minds of people around them, making them forget the user was there and allowing them to move around without being noticed, even if they were in plain sight. Unlike other ways of hiding, droids and other non-living things couldn't be tricked by a mind trick.
The beginning of the cloaking skill has been lost over time, but the Jedi Order studied this rare ability as early as the Great Sith War, where it was called an Alter ability. The Order's Great Holocron mentions Juhani, a Cathar Jedi Knight who was said to be naturally good at it. Also, Darth Traya, a Jedi Master who became a Sith Lord, liked this skill because she thought that how people saw things was just another way to control them. Traya and her other identity, Kreia, used this skill to move around without being seen by friends or enemies.
For many years, the Jedi Order kept the knowledge of this skill in the Great Holocron, which was stored in the Archives of the Jedi Temple on Coruscant. Tholme, a Jedi Master, taught the cloaking skill to his Padawan, Quinlan Vos, who later taught it to Aayla Secura. Anakin Skywalker, the famous Knight who later became the Dark Lord of the Sith, learned this skill during the Clone Wars and used it to destroy the cortosis droid factory on the planet of Metalorn. Also, as Darth Vader, he might have used this ability to stay hidden on Bespin before fighting Luke Skywalker, but Luke could still sense his presence.
Darth Maul was trained to hide himself from anyone he was hunting, so he probably knew this skill. He once successfully got into the Kaldani Spires Residential Apartments, where the police were investigating.
When the Galactic Empire disbanded the Jedi Order at the end of the Clone Wars, some survivors kept the skill alive. Maris Brood, a Padawan, became very good at hiding herself, using it with Force-enhanced speed during her fight with Starkiller, a Sith assassin, but she was eventually defeated. Jin-Lo Rayce, a Jedi, taught this skill to members of his secret group, the Agents of Ossus, so they could avoid being caught by the Inquisitorius.
While helping Mara Jade save her boss, Luke Skywalker used this power to make three men not notice him stealing Imperial clothes. Members of the reformed Jedi Order later found the Great Holocron and the teachings inside, relearning the skill that had been lost for many years. During the early days of rebuilding the Order, Jaden Korr, a Jedi, was somewhat skilled in this ability, being able to distract people while he sneaked around.
Besides the Jedi, other groups had developed similar skills. Lomi Plo, a former Nightsister from Dathomir, was good at this skill, using other people's doubts and fears to hide herself during the Dark Nest Crisis. Also, the Disciples of Twilight created several versions of this skill to fit their needs. One of these techniques, called Shadow Armor, allowed users to bend light and shadow around themselves, making their presence blend in with the darkness.