A double sentence is made up of two, a multiple sentence of more than two coordinate clauses. (This definition is not quite complete, but it will suffice for the present.)
Clauses are said to be co-ordinate, when one can be separated from the other so that each makes an independent sentence and gives an independent sense, ex. The sun rose with power, and the fog dispersed. He called at my house, but I was not at home.
Note. – Observe the difference between Sentence, Clause, and Phrase:
(1) A sentence is a combination of words that contains at least one subject and one predicate. (If a subject as predicate is absent, but “implied”, the combination, though elliptical, is still a sentence.)
(2) A sentence, which is part of a larger sentence, is called a clause.
(3) A phrase is a combination of words that does not contain a predicate either expressed or understood, as “turning to
the left” (participial phrase), “on a hill” (adjective or adverb phrase), “because of” (preposition phrase).