mean in the sentence below? And can someone please translate it?
耳に馴染みのない方も多いのではないかと思いますが、 (after that he explains the word)....
A は B ではないか is asking "isn't A (=) B?", and here used as a (stylized) rhetorical question, i.e. meaning "I think that A is B".
Since A と思いますが is "I think that A, but ...", we are also dealing with a an ellipsis (assuming you're quoting the whole sentence).
In any case, both figures of speech are very commonly used in Japanese.
Unfortunate for a straight-forward translation is that basically both parts translate to "I think that". In English, we can try to translate it like
耳に馴染みのない方も多いの ではないか¹ と思いますが …²
I think that a number of people might¹ not be familiar with [this] …²