The Solenoid Large Intensity Device (SoLID) is being planned for experimental Hall A of Thomas Jefferson National Accelerator Facility (JLab) with the capability of combining large acceptance and high luminosity. With a slate of approved high-impact physics experiments, SoLID will push JLab to a new limit as a QCD intensity frontier and will exploit the full potential of the 12-GeV CEBAF. In this paper, we present an overview of the rich physics programs that will be realized with SoLID including the tomography of the nucleon in 3-D momentum space from Semi-Inclusive Deep Inelastic Scattering (SIDIS), pushing the phase space in the search of new physics and of hadronic physics from parity-violating DIS (PVDIS), precision measurement of $J/\psi$ production from the threshold to probe the gluon field and its contribution to the proton mass, tomography of the nucleon in coordinate space with deeply exclusive reactions and more. To meet the challenging requirements, the design of SoLID described here takes full advantages of the recent progresses in detector, data acquisition and computing technologies. Potential experiments beyond the currently approved program are mentioned, including what could be explored should upgrades of CEBAF become a reality in the future.