DevOps has become an extremely popular term in recent years but it can be difficult to pin a definition onto because it means different things to different people and is implemented differently across organizations. At it's core, it is a set of principles pertaining to cross-team collaboration, business alignment, automation of manual tasks, and the application of engineering practices and tools to operations tasks (per Google SRE).
Site Reliability on the other hand is a specific implementation of DevOps. Site Reliability Engineers (SREs) are either software engineers with a good administration background or a highly skilled system administrator with knowledge of coding and automation. SREs create software solutions to remove the barriers between development and operations teams. SREs are responsible for the availability, latency, performance, efficiency, change management, monitoring, emergency response, and capacity planning of the services they support.
DevOps and SRE services focus on the core principles:
Consider me a "hired gun" that can embed into any development or operations team and contribute to their success.