The struct command creates a Maple record.  A record is a fixed-size collection of items addressable by name.  Accessing individual field values is done via the :- or [] operators.  For example MyStruct:-field1 will give you value1 as does MyStruct[field1].

The :- operator binds more tightly than [], avoiding evaluation if the name field1 happens to have another meaning in the given scope.  Conversely, [] allows evaluation to happen, which allows for name resolution, and iteration over individual fields via the exports command.

The struct command is essentially a front end to the Record command. Aside from the different calling sequence, the struct command differs from the Record command in that it adds a ModulePrint definition so the record is displayed nicely.