GitOps is a technique of using Git to manage infrastructure provisioning and software deployments. This technique uses many of the features of Git such as Pull Requests to manage and trigger deployments, and allows "diffing" (looking at the difference between commits) to view the differences between deployments.
DevOps is more of a culture or philosophy. It is not tied to the specific tool Git. Instead, DevOps is the joining of Development (Dev) and System Operations (Ops). Often continuous integration and continuous deployment are big focuses of companies that invest in a DevOps culture.
A company that has a DevOps culture may choose to use a technique like GitOps to manage their infrastructure. They may choose to use other tools though.
Note: DevOps is not a process. It is a culture. GitOps is a specific System Operations (ops) process tied to a specific tool (Git). A company that uses GitOps may not have a DevOps culture. Conversely, a company that has a DevOps culture may not use GitOps.
