After each ionic step and at the end of each job a file CONTCAR is written. This file has a valid POSCAR format and can be used for 'continuation' jobs.
For MD-runs (IBRION=0) CONTCAR contains the actual coordinates, velocities and predictor-corrector coordinates needed as an input for the next MD-job.
For relaxation jobs CONTCAR contains the positions of the last ionic step of the relaxation If the relaxation run has not yet converged one should copy CONTCAR to POSCAR before continuing. For static calculations CONTCAR is identical to POSCAR.