Long sentences that contain many subordinate clauses are characterized in terms of hypotaxis, the Greek term meaning the grammatical arrangement of "unequal" constructs (hypo="beneath", taxis="arrangement").
Thus anytime two syntactic units are in a head-dependent relationship, subordination obtains.
Two units or more are coordinate to each other if there is no hierarchical relation between them and they have equal functional status, e.g.
Most theories of syntax represent subordination (and coordination) in terms of tree structures.
The constituency relation is again shown in the a-trees on the left, and the dependency relation in the b-trees on the right: The constituency trees show that both parts of the coordinate structure project up to the root node of the entire tree, and the dependency trees illustrate that each word again projects just a single node.
Both representation formats illustrate the equal status of the coordinated units insofar as they are placed on the same level; they are equi-level.
From an organizational point of view, subordination is grouping words together in such a manner that includes hierarchical and linear order, and coordination is grouping words together only in terms of linear order.