Wikipedia provides the following definitions:
Metrical rhythm, by far the most common class in Western music, is where each time value is a multiple or fraction of a fixed unit (beat, see paragraph below), and normal accents reoccur regularly, providing systematic grouping (bars, divisive rhythm).
Measured rhythm is where each time value is a multiple or fraction of a specified time unit but there are not regularly recurring accents (additive rhythm).
Free rhythm is where there is neither.
I'm confused by this definition of 'measured rhythm' because it makes it sound like an additive rhythm is a measured rhythm. And I thought 7/8 was an additive rhythm because of its 2-2-3 grouping structure for the beats, so (2+2+3)/8, thus additive.
Is 7/8 an example of measured rhythm or metrical rhythm? If it is a measured rhythm, why do people call it a meter? What distinguishes a measured rhythm from a meter with unequal groupings like 2-2-3?