Training Center XML (TCX) is a data exchange format introduced in 2007 as part of Garmin's Training Center product. The XML is similar to GPX since it exchanges GPS tracks, but treats a track as an Activity rather than simply a series of GPS points.
Training Center XML (TCX) is similar to GPX in that it exchanges GPS tracks, but differs in its approach by considering a track as an Activity rather than just a collection of GPS points.