Telepathy is the abitlity to read another person's mind and is one of the most common forms of laran, along with Empathy, the ability to sense the emotions of others. When laran is referred in the books without other qualification, it is taken to mean some greater or lesser form of telepathy.
Telepathic contact between a telepath and a non-telepath is not really possible unless you have one of the Gifts that allows that kind of contact, Alton or Ridenow. The telepath will perceive only vague feelings or strong emotions of the non-telepath.
A trained telepath can block his or her mind so that another telepath can not read their thoughts, among Darkovans it is considered a bad manners even a crime to read the thoughts of others especially without their consent. Keeping ones mental barriers properly raised to not inflict your private thoughts upon others is usually the norm and taught to those who have emerging laran.
The onset of laran can often be painful and traumatic, threshold sickness, many times during this period a young telepath with read stray thoughts or unconsciously raise their own barriers. Once in place these unconscious barriers are difficult to lower and inhibit the development of an individual's gifts, sometimes when this happens kireseth can be used to lower them or someone possessing the Alton gift can smash through the barriers but this can be extremely dangerous.
Once given and keyed into a matrix a telepath can communicate with another across vast distances, sending and receiving thoughts and messages.