From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Telepathy (テレパシー, Terepashii) is a supportive technique used by many fighters.
Telepathy was a way to communicate with others using one's mind. Several of the Z Warriors had demonstrated this ability as well as many other characters throughout the series. North Kaio was possibly one of the most famous users of this technique as he was able to speak with people all across the universe, and could even speak to several people at one time. It can be assumed that he taught it to Son Goku while he trained with him in the Next World, who in turn taught it to the other Z Warriors.
The ability to communicate telepathically did not seem to be hindered by time dilation, as Piccolo was able to talk to Son Goten and Trunks Brief when they were in the Hyperbolic Time Chamber despite him being outside of it.
- Babidi - Uses Telepathy to communicate with Earth's populace regarding the location of Son Goten, Trunks Brief, and Piccolo.
- Bon Para, Don Para, and Son Para - The three brothers use Telepathy to communicate Lood's weakness to Goku and coordinate a synchronized assault against the Machine Mutants.
- Chaozu - Uses it to talk to Tenshinhan and Crane Hermit.
- Crane Hermit - Talks to Tenshinhan and Chaozu.
- Dr. Gero and Dr. Mu - They brainwash Android 17 using Telepathy.
- Nappa - Uses it to communicate, agreeing to Vegeta's orders while visiting Planet Arlia.
- North Kaio - Uses it to talk to Goku and his friends to warn them about trouble. People can also touch his back and communicate with any desired person.
- Piccolo Daimao - Uses it to contact Tambourine and Cymbal.
- Piccolo - Talks to Gohan several times. Most famously when he was attacked by Android 20, and when he was about to sacrifice himself to save Earth in DBGT.
- Son Gohan - He uses it to tell Chichi to not "...worry mom, I'll be back soon!" (DBZ Episode 11)
- Son Goku - Uses it to command Great Ape Gohan to attack Vegeta and to stop Kuririn from killing Vegeta as he is trying to escape.
- Son Pan- She uses this to communicate with Goku underwater during their fight against Haze Shen Long.
- Tenshinhan - Uses to talk to Crane Hermit and Chaozu.
- Turtle Hermit - Uses the technique, rivaling Crane Hermit.
- Vegeta - Uses it to communicate orders to Nappa while visiting Planet Arlia and to read Fat Boo's memories while inside Super Boo's head.