Skype private conversations uses the industry standard Signal Protocol, allowing you to have end-to-end encrypted Skype audio calls, send text messages, image, audio, and video files. The content of these conversations is hidden in the chat list notifications to keep the information you share private. Private conversations are not available in Skype on Android 4.0.4 - 5.1.
Note: Private conversations can only be accessed on one device at a time.
For technical details about the implementation of private conversations, view the private conversations white paper.