A mixed CD of personal songs made by one person that he or she is too ashamed to share with his or her buddies. The most common type of confidential mix tape is a CD full of love songs for Valentine's day.
Duder 1: "You're gonna leave the CD in her car so when she starts them shits up in the morning it'll start playing? Nicely done. When do I get to hear it."
Duder 2: "Never doggy! That's a confidential mix tape for sure."
Duder 1: "You're such a bitch dogg. I gots to hear your amazing love ballads."