A genset locomotive is a locomotive in which a number of smaller diesel engines are used rather than a single large engine.
The term is short for "generator set.
"[1] A genset uses one to three small diesel engines to provide power.
An operator is able to activate each engine as needed, with more than one engine gensets activating one for light work and activating more for heavier work, with excess engines turned off when the extra power is not needed.
[1]