Someone who spends a great deal of time with some one they may or may not be interested in. This person can flirt without trying to hook up or may already be dating the person they are caking with. This person is engaging in flirtatious actions that include talking intimately up to but not including having sex (of any form).
Yeah I was on the phone with him last night, you know what a caker I am.
She was hugged up with him mighty close last night. What a caker.