[coin]

I dislike abbreviations for this exact reason. Both your and the above responses are different. Clearly it's not well known abbreviation.

[zellyn]

Personally Identifying Information. It's pretty common to anyone who works with PII. Also the top Google search result for PII.

[andrewcooke]

sorry, i probably shouldn't have replied. difficult to know whether the context is "quickly help me understand what this means" or "give me a precise answer", but for the web, with a technical audience, i should lean more towards the latter...