[rdhatt]

These are my mnemonics, pretty sure I'm not too far off though:

  r = RAM.    Instances are biased toward having more memory.
  i = I/O.    ... have fast SSDs.
  d = DISK.   ... lots of disk space.
  x = XL.     ... lots of RAM
  g = GPU.    ... have GPU hardware

...and of course now I realize this is already answered on SO. I'm keeping mine though.

https://stackoverflow.com/a/56880093

[gazby]

This is definitely helpful, though I think the SO question showcases fairly well why someone would want the summary on the web page: Several are ambiguous and if you're not regularly exploring new instance types you're going to forget this or fall behind in your awareness of new types.