Rare-earth tri-tellurides (RETe3, RE = Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm) are materials with 2D electronic character and have a charge-density wave (CDW) phase as a stable ground state at room temperature (T). The electronic ground state is changed upon modifying pressure (P), T and magnetic field (B). With decreasing T different types of CDWs appear and below 10K different magnetic phases emerge, e.g. in case of TbTe3 three types of magnetic phases appear. At T ~2K, when pressure is applied it shows superconductivity (SC). RETe3 have a rich P-T phase diagram but poorly investigated system. In this proposal we focus on TbTe3 at T =10-1K, where different magnetic phases and SC upon P are present. Muons are an ideal probe of the coexistence of magnetism and SC. Muon measurements as a function of P and T would dramatically increase the understanding of this material.