A mental or visual masturbatory aid; someone who you look at (a picture of) or think about when you masturbate. From the Japanese term okazu, which originally referred to a side dish that is eaten with one's rice, but acquired a second, sexual meaning (not unlike bukkake).
1) Hikari isn't innocent! She uses Toji as a side dish every night -- and sometimes during the day!
2) Mmm! That guy is the best side dish I've never tasted!