It's truck. Under the discussion of movement types, per 8.3:
8.3B-Motorized units generally have all
personnel and weapons carried or towed by
vehicles. There are two primary classes and one
• Trucked units are the standard in the game,
and are sometimes referred to generically as
“motorized.” They have enough vehicles to carry
the entire unit, but not enough to assign one to
each individual sub-unit. Trucked units generally
dismount some distance from combat.
I take references to motorized movement allowances as meaning trucked unless a unit is marked as tracked or it specifically says tracked.