If two dancers are on the ice dancing side by side, they are coordinated; they are equal partners.
In grammar, the idea of coordination is the same. The same sorts of clauses can be joined by coordinating conjunctions such as and, but, or, nor. Coordination means 'of the same order/level': I sketch and I also paint (joining two simple sentences) OR He built the robot because some jobs in the factory were dangerous for humans and because there had been a lot of accidents (joining two adverbial clauses–because... and because).
If we join principal clauses together with a coordinating conjunction, that creates compound sentences. Of course, complex sentences can also be compounded.
You will realize now why we use the term 'subordinate clauses'. The term helps us to see the difference between lower order, dependent clauses and clauses of the same type (coordinate clauses) joined by words such as 'and' and 'but'.