PDFs The internal structure of nucleon/nuclei in terms of quark and gluon degree of freedom. "Initial conditions"in ep/eA/pp/pA/AA collisions. Collinear parton distributions. k~xp DIS: (k)<2 The simpliest ones:unpolarized integrated parton distributions:f(x),G(x)PDFs The internal structure of nucleon/nuclei in terms of quark and gluon degree of freedom. "Initial conditions" in ep/eA/pp/pA/AA collisions. Collinear parton distributions. The simpliest ones: unpolarized integrated parton distributions: f(x), G(x)