Another more speculative possibility is that cosmic strings could come from the tiny vibrating strings of string theory. Some string theory models propose that strings could have grown to colossal proportions during the initial rapid expansion of the cosmos. Differences in the tension of these kinds of cosmic strings and in how string loops break away would create a unique gravitational-wave signature distinguishing them from other kinds.

Not far enough down the line to understand either theory but "string" is overloaded.