High Quality Content by WIKIPEDIA articles! In general relativity, a frame field (also called a tetrad or vierbein) is an orthonormal set of four vector fields, one timelike and three spacelike, defined on a Lorentzian manifold that is physically interpreted as a model of spacetime. The timelike unit vector field is often denoted by vec{e}_0 and the three spacelike unit vector fields by vec{e}_1, vec{e}_2, , vec{e}_3. All tensorial quantities defined on the manifold can be expressed using the frame field and its dual coframe field. Frames were introduced into general relativity by Hermann Weyl in 1929.