If you're trying to identify what device an IP address is assigned to, Steve N. has the most accurate method.
I usually google the MAC address and see if that will give me a clue. For example, I found that one device I couldn't identify had a MAC address that is in a range associated with Sonos. That made me realize I'd forgotten my Sonos was on the network.
Some routers will allow you to add or edit device names. I believe most/all Asus routers do it, and at least some Linksys routers do.