Internal Combustion Engine (ICE)
An engine that burns fuel internally to produce motion. The default fleet powertrain, and the thing everything else is now defined against.
An internal combustion engine burns gasoline, diesel or a gaseous fuel in cylinders to turn a crankshaft. It has been the fleet default for a century and remains most of what a public fleet operates.
The term is used much more now than it used to be, and almost entirely as a contrast. Fleet documents say ICE where they once just said vehicle, because an electrification plan needs a word for what is being replaced. Where a policy or a grant condition uses it, read the definition carefully: some treat hybrids as ICE because they burn fuel, others exclude them, and the difference can decide whether a purchase qualifies.