Hello Gemini AM means Ante Meridiem (Latin for "Before Noon") PM stands for Post Meridiem (After Noon).

Just to add to Marie-Hélène's answer... Since 'meridiem'='middle of the day'='noon', it's useful to remember that it's 12PM (midday) which follows 11AM (and 12AM, midnight, follows 11PM). So the switch to AM/PM happens at the 12th hour, not on the first hour. It confuses us sometimes too. ;) If in doubt, just say 'midday/midnight'!

am means after morning..and pm means pre morning........{just kidding yaar}