Or from Latin baculum a stick, because the squire would practice with a staff, not a sword. Meaning evolved from knight in training to young unmarried man (early 14c.). Bachelor party as a pre-wedding ritual is from 1882.
A transcutaneous electrical nerve stimulation (TENS) unit is a device that sends small electrical currents to targeted body parts. These currents are used to relieve pain. Some TENS units are designed for use in a hospital or healthcare facility.
Medical professionals have relied on the safety of TENS technology for decades because of its effectiveness in relieving pain without issues from prolonged, targeted use because it can be used in combination with topical or oral drug therapies, when used as directed.