Stabilisation de la formule des traces tordue VI: la partie g\'eom\'etrique de cette formule

This paper is one of a series whose goal is to stabilize the twisted Arthur-Selberg's trace formula. Here we define the objects appearing in the geometric side of the twisted trace formula. We define also the similar stable and endoscopic objects. We state the principal theorems concerning the stabilization of this geometric side. The proofs will be given in forthcoming papers.