Telepathy was the very basic ability to mentally communicate over small or vast distances with other individuals.
Every Force user, Jedi or Sith, was able to use it. The range of telepathy itself is theoretically infinite, but the telepath must be able to sense the presences of those they wish to contact. Thus, communicating with non-Force-sensitives became nearly impossible over distances greater than a handful of kilometers, and the typical upper limit for Force-sensitives was approximately 1,000 kilometers. However, individuals who were siblings, related, lovers, or lifelong friends, or who were once master and apprentice, were known to communicate across ranges far longer than that, and, in extreme cases (such as the twin bond between Jacen and Jaina Solo), the link apparently had no limit.
Generally, a Force-user was not telepathic enough to truly read the thoughts of other beings, but only the emotions and images of them. This form of basic telepathy was more commonly known to be Force empathy. It should be noted that while every Force-adept was able to use it, very few were actually skilled enough to commit in actual telepathic conversations. Most Force-sensitive individuals could only exchange short four or five-word sentences to those that they shared close bonds with. Usually, Jedi employed telepathy only to read the states of minds or engage in silent communications. Eye contact, in part, allowed a user to have less difficulty in focusing on a target's thoughts. A very skilled user could isolate their own brain waves, intercept stray thoughts, screen multiple minds simulatenously, whisper across space, yell without noise, keep secrets, and uncover the truths under layers of deceits and hidden memories. Adept pilots could even be able to seek information from other stars so as to navigate a starship through hyperspace without use of a nav computer. Moreover, telepathy also gave its user an advantage in combat, being able to easily predict the next movement of an opponent, and furthermore to taunt and confuse opponents by echoing their voice in their head in every direction, masking the users position.
Some species, such as the Iktotchi, the Hortek, the Quermians, Zeltrons, Umbarans, and the Draethos, had evolved a natural telepathic ability, common even to those of their number who could not touch the Force. When trained as Jedi, their natural talents were often magnified a thousandfold or more. This was the case with Saesee Tiin, whose natural prowess in the ability caused him great discomfort during his years as a Padawan. It was not until he was trained by Jedi Master Omo Bouri that he learned to better control his telepathic sense. Some Lamproids exhibited natural telepathy, although this was not a species-wide trait.
Because telepathy was such a basic use of the Force, Luke Skywalker was able to employ it to reach out to his twin sister Leia Organa and call for her help during the Occupation of Bespin. Dark Lord Vader then (as Luke and the group were escaping) called out to Luke to again convince him to join him and embrace the dark side. The fact that the three were related allowed them to reach out over even greater distances.
Neural Storm was a telepathic ability that used psychic energy to overload a victim's neural network, causing extreme but momentary disorientation.