A glowpane was a handheld computer device.
Rebecca Jae Sisko owned a glowpane. Rebecca would use the device to write humorous messages and riddles to her parents Benjamin Sisko and Kasidy Yates, such as "When is a door not a door?", "You are what you read" and "Parents Stay Out!, and hang the glowpane on the entrance panel to her room in Sisko's quarters on the USS Robinson. (ST - The Fall novel: Revelation and Dust, DS9 novel: Sacraments of Fire)