A tendon was a tough band of fibrous connective tissue capable of withstanding tension that usually connected muscle to bone.
In 2373, after having sex with Grilka, Quark was left with strained tendons, along with several other injuries. (DS9: "Looking for par'Mach in All the Wrong Places")
Also that year, Marayna pulled a tendon in her leg and placed Harry Kim's hand upon it, much to his embarrassment. (VOY: "Alter Ego")
In 2374, a a member of an unknown alien race was found missing all its insides, including tendons. (VOY: "Hunters")