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, believing she had pulled a tendon in her leg, placed Harry Kim's hand upon it, so he could feel it. He remarked that it was like a knot. Embarrassed by his predictable reaction to her, Kim declined to discuss the matter further with Tuvok. (VOY: "Alter Ego")
In 2374, a buck-toothed alien was found missing all its insides, including its tendons. (VOY: "Hunters")