A load cell is a force transducer, i.e. a sensor that measures the applied force. Other common terms used for "load cell" are "load washer" or simply "force sensor".
There are various ways to measure forces. The very common strain gauge technology requires an elastic measuring element in the load cell to capture the applied force. Load cells based on the piezoelectric measuring principle comprise piezoelectric measuring elements that generate a charge under load. The piezoelectric element functions simultaneously as a sensing element and as a transduction element of the acting force. A downstream charge amplifier converts this into a process signal that can be evaluated.