AM may refer to any of the following:
1. When referring to audio or a signal, AM is short for amplitude modulation. AM is a broadcast with the capability of broadcasting in a wide area, but in a lower quality when compared to FM.
2. When referring to time, A.M. is short for ante meridiem, which is Latin for "before the middle of the day" and can also mean "after midnight." This time is between 11:59 P.M. midnight and 11:59 P.M. noon in a 24-hour time clock. In other words, A.M. is in the morning and P.M. is in the afternoon and at night.
Should I uppercase or lowercase A.M. in my writing?
The capitalization of A.M. all depends on the style guide you're following and your type of writing. With formal writing and according to the Microsoft Manual of Style you should be using uppercase and include periods, as we've done on this page. Other style guides like the AP Stylebook, Chicago Manual of Style, and Merriam-Webster's Collegiate Dictionary all recommend writing a.m. as lowercase with periods.
If you're writing for a company or organization, follow their style guide or the rules in the style guide they follow. If no style guide is followed decide on one form of style and be consistent in all your writing.
Should I use periods when writing A.M. in my writing?
As with the capitalization of A.M., using periods or omitting periods all depends on the style guide you're following or personal preference. Many people use periods because "am" is a word by itself and using it with time may introduce confusion. Others prefer the look and ease of writing "am" without periods.
3. On the Internet .am is a top-level domain.