What's the difference between EFVS and CVS?
The FAA recognizes 4 'vision' systems; enhanced vision system (EVS), synthetic vision system (SVS), combined vision system (CVS), and enhanced flight vision system (EFVS).  

EVS and EFVS use either passive or active sensors on the aircraft to enhance the crew's vision of the approach. SVS uses a database to generate a synthetic view of the terrain in  front of the aircraft. CVS combines features of EVS or EFVS and SVS.  

It's all spelled out in AC 20-167A Airworthiness Approval of Enhanced Vision System, Synthetic Vision System, Combined Vision System, and Enhanced Flight Vision System Equipment