A touch switch is a lightsaber activation switch that allows you to turn on the lightsaber purely by touch, rather than by pressing a button. All you need to do is graze the touch switch with your finger, and the lightsaber will activate.
Watch What is a touch switch? (Lightsaber Terminology) on YouTube
Custom saber company Electrum Sabercrafts is know for using touch switches on their lightsabers. To activate an Electrum Sabercrafts lightsaber, like this Torrent, slide your finger up the touch switch toward the emitter. To deactivate, reverse the process.
A nice bonus feature for Electrum Sabercrafts touch switches is the switch activates a series of small secondary lights as you run your finger up or down the touch switch. The secondary lights are a fun effect.
Electrum Sabercrafts is known for using touch switches–touch switches are one of their signature features. A few other lightsaber companies occasionally use touch switches on their lightsabers as well, however, touch switches are not as commonly used as other emitter switches (e.g. guarded switches, AV switches, tactile switches, etc.).
As with many lightsaber features and accessories, some people like touch switches and others do not. People who like touch switches enjoy the ease of use and cool visual effects of the switch. People who don’t like touch switches fear activating the switch unintentionally during dueling and dislike the fact that the switch cannot be activated while wearing gloves.