Site to Site VPN :
A site-to-site VPN allows offices in multiple fixed locations to establish secure connections with each other over a public network such as the Internet
DMVPN :
DMVPN is a solution to build an on-demand full-mesh of secure IPSec VPN tunnels.
DMVPN allows distributed locations to discover and communicate directly between each other.
New sites register with head-end (Hub) without requiring any configuration changes at the head-end.
This enables zero-touch deployment of new sites.
https://www.cisco.com/c/en/us/products/security/dynamic-multipoint-vpn-dmvpn/index.html