The first question is how much of a vehicle the goods need
If a consignment fills a vehicle, or comes close enough that selling the remaining space is not worth the trouble, it is a full load. The vehicle goes from collection to delivery and the goods are not touched in between.
If it does not, the goods will share a vehicle with somebody else's, and that changes what happens to them. Sharing means being loaded alongside other consignments, and usually means passing through at least one handling point where loads are separated and recombined.
The threshold between the two is commercial rather than physical. A part load large enough that no realistic combination of other cargo will fill the vehicle around it is being priced as a full load whatever it is called.
The second question is how much handling the goods can take
Every additional handling point is an opportunity for damage. Goods that are well packaged, palletised, stackable and robust move through a consolidation network without difficulty. Goods that are fragile, awkwardly shaped, unstackable or poorly packaged do not, and the saving from sharing a vehicle can be smaller than the cost of one damaged item.
This is the question shippers most often skip, because packaging feels like a decision that was already made. It is worth re-asking whenever a consignment is being moved from a dedicated vehicle to a shared one for the first time.
The third question is how fixed the date is
A dedicated vehicle runs to the movement's own schedule. A shared vehicle runs to the network's: departures, hub cut-offs and delivery rounds that exist whether or not one particular consignment is ready.
Where a delivery date has real tolerance, the network's schedule is rarely a problem and the saving is real. Where it has none — a production line, a fixed installation slot, a penalty — the value of controlling the vehicle usually exceeds the cost of it.
Where each service lands
Full truck load suits consignments that need the whole vehicle, that cannot take handling, or that have a date with no tolerance. Less than truckload suits part loads on a direct or lightly handled routing. Groupage suits smaller consignments moving through a consolidation network, and is the right description when the network — rather than the consignment size — is the defining feature.
Express suits movements where speed is the requirement and the price reflects it, generally with a dedicated vehicle and a direct route. Pallet freight suits standardised, palletised consignments that fit a network built specifically around handling pallets.
These are not five rungs on one ladder. They are answers to different combinations of the three questions above, which is why the useful conversation with a forwarder starts with the cargo rather than with the service name.