What exactly does ‘Secure Boot’ mean for embedded systems?

A variety of published and unpublished security incidents in the last few years have driven the software industry to focus on the security of the boot process for microprocessors and embedded processors. Solutions to the problem of insecure boot processes vary enormously depending on two major inputs: whether the ‘secure boot’ solution is trying to protect the boot code itself from loss and reverse engineering, and what threat the ‘secure boot’ solution is trying to address.