Cello external mount. The long cable (pictured) is a detachable model with instrument jack. Short cable also available, for attaching to the tailpiece.
This is an excellent pickup for cello which comes in two styles for mounting. One has a short cable (12") with jack included for mounting to the tailpiece using electrical tape or zip-tie and can be left on the instrument. Requires soldering to jack once cable length is fitted to instrument.
The other model uses a longer pre-wired cable extending away from the instrument and is generally preferred for removable mounting. This is often the choice of ensemble/orchestral musicians.