Nonessential information is the information not necessary to the main point of the sentence that uses a comma or commas to separate from the rest of the sentence.
WRONG: The domestic cat of which there are more than 40 breeds, is a member of the feline family.
RIGHT: The domestic cat, of which there are more than 40 breeds, is a member of the feline family.
** To determine if a portion of text is nonessential information, try reading the sentence without those words. If the sentence makes sense, the words in question are probable nonessential.