In the Federation standard system of planetary classification a class T planet is used to categorize some types of gas giants.

In 2376, the Delta Flyer came in contact with a dark matter lifeform in a class T cluster and was disabled. Captain Kathryn Janeway took the Flyer to a nearby class T gas giant with orbital rings, including one that was radiogenic, hoping to use those particles to reinitialize the Flyer's warp reaction. She eventually set off a chain reaction inside the rings with the Flyer's phasers to deter more dark matter lifeforms. (VOY: "Good Shepherd")

Planetary classification
D • H • J • K • L • M • N • T • Y • Other classes