It could mean a small portable box that can carry a few tools to a project location or a large storage system set on casters.
Many have a removable tote tray that sits on a flange inside the lip of the box, with a single larger compartment below.
A plastic toolbox laden with tools can weigh the same as a comparable steel box does when empty.
Metal boxes are also subject to rusting and their sharp edges can mark the surfaces of things they are banged against.
Metal is, however, known for being stronger than plastic, so one should balance its disadvantages against the need to withstand abuse and support the weight of many tools.
Portable chests are a type of tool storage that is small enough to carry, but has drawers to organize contents.
Used as portable work stations, some of the larger types are self powered and propelled, for example, pit carts in automobile racing.