ante meridiem(=before noon) 午前,上午;

AM:(0:00-12:00)ante meridiem or ante meridian---上午

PM:(12:00-24:00)post meridiem or post meridian---下午

For example, in Baltimore, some schools take attendance at 10 a.m. rather than 8 a.m. because theyknow if kids show up at all, they come in late and would be counted absent. 例如，在巴尔的摩，一些学校在上... 上午是AM。