String break angle is the angle a string makes where it bends over a nut or a bridge. The string break angle is a factor of bridge height, neck pitch, tailpiece height, action or a combination of these (Siminoff, 122).
Conversely, string tension is the amount of compressive force placed on an instrument from the tailpiece to the peghead.
Core wire in musical strings is the inner most section of a wound string. Most core wires are hexagonal in shape versus round to help lock the wrap or cover (the outer part) of the wire in place thus preventing unraveling. Classical guitar strings uses a nylon filament core.