SRE is an exciting field. As mentioned earlier, it has evolved from a long line of roles and, as it is a relatively new field, its definition is steadily changing. SRE is an extension and evolution of many past concepts and, as such, concepts relevant to SRE apply to many roles, including but not exclusive to, backend engineering, DevOps, systems engineering, systems administration, operations, and so on. Depending on the company, these roles can involve very similar or very different responsibilities. The point is that, no matter what your job title is, you can apply SRE principles to your role.
In an attempt to define the field, we can learn a lot from its full name, Site Reliability Engineering: