Time zones
Why are time-zone abbreviations so ambiguous?
CST, IST and BST look concise but can name different places and rules. A city or IANA zone is safer.
Three letters are not enough context
CST can refer to Central Standard Time in North America, China Standard Time or Cuba Standard Time. IST can mean India, Israel or Irish Standard Time. BST is used for British Summer Time and Bangladesh Standard Time.
Summer makes it worse
Some abbreviations change when daylight saving begins, while others do not. A meeting invitation saying “3pm CST” may be unclear even to people in the same country if it is sent months ahead.
Use a city, date and zone when it matters
Write “3pm in London on 8 October” or include a recognised identifier such as Europe/London. For technical systems, IANA names are designed to distinguish locations with different clock histories; abbreviations are chiefly display labels.