A compact vessel built for travel through time, such as the 31st-century craft recovered by Enterprise in Future Tense and the stolen 26th-century pod in A Matter of Time.
A time pod is a small craft whose purpose is to carry a pilot through time. Two notable examples appear in Star Trek.
In The Next Generation episode A Matter of Time, Berlinghoff Rasmussen arrives aboard the Enterprise-D in a pod and claims to be a historian from the 26th century. He is really an inventor from the 22nd who stole the craft from its true owner and hopes to take 24th-century devices home with him.
In the Enterprise episode Future Tense, set in 2152, Archer's crew find a tiny ship adrift with a dead pilot of mixed human ancestry. It is far larger inside than outside and comes from the 31st century. Suliban and Tholian ships fight to seize it before it vanishes back to its own time.