One dimensional (1D)
A system where all dependent parameters can be described in terms of a single independent parameter. For a resonator this means that both the shape and performance parameters depend only on a single coordinate value. For example, if a resonator is oriented along the Z axis, then everything about the resonator at any Z location can be predicted just by specifying the Z location. (Note: the predicted performance will not necessarily be accurate if any underlying assumptions are violated -- for example, an assumption that the resonator is slender if it is not.)
Also see axisymmetric.