Confused about meaning of SE and EX releases in cisco IOS

I have been looking into this for a while now, but I can’t find an explanation anywhere (the closest I could find was in wikipedia and cisco )
The switch is a 2960s that I need to stack to a 2960x (so I need the exact ios versions on both), I can download these two versions for the 2960S 15.0.2-EX5(ED) and 15.0.2-SE10a(MD)

Basically it seems to say that:

  • S Consolidates mainline, E, and other S, which supports
    high-end backbone routers, and fixes defects.
  • E Targets enterprise core and SP edge, supports
    advanced QoS, voice, security, and firewall, and fixes

But what means SE? It’s a mix of S and E? What means the X in EX?