What is the definition of "Boo"?

[John]

thanks for the comments, and if someone called you as his boo, meaning that, you're important to him? but what if at the same time he never talked to you, or seldom reply your msgs and never took initiative to tell you anything or send you any msgs for almost 2 months? and the replies from him would be like a single word or only came once after so many msgs from you?