By server, I mean a computer that is fit for an enterprise data center.
Different people will no doubt look at this question from different angles. If you are into computer technical specs, you probably would be quick to point out the difference in the number and type of processors they support, the number and type of expansion slots they support, the difference in fault tolerance, and so on and so forth.
I spent a few years doing testing and stress testing for a living, and have been conditioned to look at the question from that perspective. As such, my answer is that a server is not supposed to crash under stress test, whereas you probably don’t want to subject your desktop under severe stress workload (unless of course you are a manufacturer or work for a test lab).