Both BUILD and RELEASE are end products of software development processes and both helps the developer and QA team to deliver reliable software that's why are similar.
But both still have the differences and these are:
1. BUILD is still running in testing that is released to testers for testing. But, RELEASE is no longer with testing and release to Customers/Clients.
2. BUILD occur more frequently whereas, RELEASE occur less frequently.
3. BUILD is process of converting sourece code in to executable
code (.exe) whereas, RELEASE is a process of delivering the project to client