orthogonal adj.
[from mathematics] Mutually independent; well separated;
sometimes, irrelevant to. Used in a generalization of its
mathematical meaning to describe sets of primitives or
capabilities that, like a vector basis in geometry, span the
entire `capability space' of the system and are in some sense
non-overlapping or mutually independent. For example, in
architectures such as the PDP-11 or VAX where all or nearly all
registers can be used interchangeably in any role with respect to
any instruction, the register set is said to be orthogonal. Or,
in logic, the set of operators `not' and `or' is orthogonal, but
the set `nand', `or', and `not' is not (because any one of these
can be expressed in terms of the others). Also used in comments
on human discourse: "This may be orthogonal to the discussion,
but...."