Does a carry-on count as a backpack?

Excuse me, I'm a bit confused about the luggage regulations. Could you please clarify for me if a carry-on bag is considered the same as a backpack? I'm trying to pack for a trip and want to make sure I'm adhering to the airline's guidelines correctly. I've noticed that some airlines have specific rules about the size and weight of carry-on items, and I'm wondering if a backpack falls under the same category as a traditional carry-on suitcase. Thank you for your help!