What is the difference between 'truck,' lorry', and 'van'? Can I use them interchangeably? I didn't see them in any context but I am a little bit confused about how to use them. Thanks for answers.
They are all meant to mean different classes or sizes of goods vehicle. However, there are differences between US and British English. As I am British, I will use the definitions in BrEng as a starting point and note the US variations that I'm aware of. I welcome any comments to help me improve the definitions for US English.
A van is the smallest - the sort of vehicle a sole tradesman, such as a carpenter, might drive. There are different sizes of van, but they usually have just 4 wheels and don't require any special licence to drive them because they are not so much bigger than a car.
In British English, a truck is the middle class of these vehicles. An example of these might be the kind of vehicle used by delivery services like UPS, or what you would hire if you were moving home. They are large, but not so large that they couldn't travel on a suburban street. Again, most of these can be driven on a British car driver's licence. I note that in US English they call refuse collection vehicles "garbage trucks", which are a similar size and class.
A "lorry" is the largest, and may also be a called an articulated lorry or a heavy goods vehicle (HGV). These normally only travel on major roads and carry the largest quantities. In England, you also have to hold a special licence to drive them, making them a different class of vehicle. I note that in US English these seem to be called "trucks" and those who drive them "truckers".
To sum up - "van" and "lorry" are clearly different and refer to the smallest and largest vehicles of these classes. "Truck" seems to be a more generic word to describe the harder-to-define middle-size vehicles. Some of those middle-sized vehicles may get referred to as "vans" if they are not particularly large; likewise, some lorries get called "trucks".
In Canada and the U.S., lorry is generally never used.
Van is a vehicle that is about the same size as a pick-up truck but that has enclosed sides and a roof in the back for cargo. Many are passenger vans which have 3 or 4 rows (usually of bench seats) and hold anywhere from 6 to 15 people). Sometimes, the benches are removable and you can switch to a cargo van, though some cargo vans have no windows in the back / sides (except for passenger seats) and are not appropriate for people. Some are used by tradespeople (e.g., electricians, cable guy) to keep their supplies and tools secure. A cube van definitely has no non-passenger windows, is generally a bit bigger than a cargo van in the back, has a severely rectangular shape (cargo vans usually have rounded features), and is used for moving / delivery. A camper van is like a passenger van (usually windows in the back) but with a bed, stove, fridge (sometimes a shower / toilet) and often a popup roof for extra height.
A truck is usually for work, though a pick-up truck can also be for fun (e.g., carrying snowmobiles or towing a boat). A pick-up (truck) is a cab (1 or 2 rows, usually a bench for the 2nd row) with an open bed in the back (with about 2 foot side-walls and a gate that usually fold out/down to gain access).
A transport-truck (or semi-truck, semi, rig) [lorry in the UK] is a taller, bigger cab (sometimes with sleeping quarters in the 2nd row), towing 1 or 2 (sometimes 3) detachable shipping-like containers (with wheels) or flatbeds (logs or pipes) or liquid containers (milk, oil, gas). In Australia, they also have road-trains between cities, which are like transport trucks, but can have more containers.
Trucks cover the range from pickup to transport, and include vehicles between cargo vans and semis in size used to transport goods within a city - usually the container part is not separable from the cab in these trucks. Then you have specialty trucks - e.g., garbage/recycling trucks, fire trucks - which are always named with the modifier.
I guess a cargo/cube van is technically a truck, but I've rarely heard it referred to as a truck.