In general relativity, we have a relativistic spacetime, and in a neighborhood of a point we take coordinates . This coordinates give rise to the coordinate frame, which is not necessarily a vielbein. We can choose a reference frame which can even be inertial. If we take a general coordinate transformation , in this new coordinates we have a different coordinate frame which is obtained from by the linear transformation (in every point) . But the vielbein is the same (what changes is its expression with respect to the corresponding coordinate frame).
Given two different vielbeins, for every point in spacetime we have a Lorentz transformation relating them
In special relativity, the spacetime is the Minkowski space, given with a preferred choice of coordinates , in such a way that the metric is , and therefore the coordinate frame is a vielbein. Moreover, it is an inertial frame. Now, if we consider, instead of a general coordinate transformation, a transformation belonging to the Poincare group, the new coordinates satisfy the same: the coordinate frame is an inertial frame. Both coordinate frames are related by an element of the Lorentz group. We can call to the coordinates obtained from this way inertial coordinates.