The SDK ( System Development Kit) is usually more complete. Such boards usually allows you to get the sense of what it takes to boot, program and run a program.
These boards can also be named demo boards, demo cards or system development kits (SDKs).
You can use those to decide whether you want to spend your time and budget on that particular CPU. Most chip manufacturers provide evaluation boards. Board Support Package for Linux or other operating systems are here to help you taking the best of it. When developing an embedded system, you will be attracted by new system on chip (SoC) with functionality that can significantly improve the overall performance of the final product.
