Slightly concerned what Leadfingers was promoting!

Agree.....never assume everyone knows what you're talking about!

In my ex-profession, PID could mean Pelvic Inflammatory Disease - or Prolapsed Intervertebral Disc - depending which department you ended up in. (which would you rather have??)
There was a convention that you would spell the whole thing out first time and thereafter resort to initials/acronyms.