Which abbreviation means "in the evening"?

The abbreviation "pm" is derived from the Latin phrase "post meridiem," which translates to "after midday." In the context of time, it specifically refers to the hours from noon (12:00 PM) until midnight (11:59 PM), encompassing the evening hours. This makes "pm" the correct abbreviation for indicating something is relevant or scheduled for the evening.

The other options represent different meanings: "qod" stands for "every other day," "prn" means "as needed," and "po" indicates "by mouth" (from the Latin "per os"). These terms are commonly used in pharmacy and medical contexts but do not pertain to specifying the evening hours.