The English-speaking world uses a 12 hour system when telling time. This means that am and pm are used to specify whether the time is in the morning (from midnight to noon) or in the afternoon / evening (from noon to midnight). For example, ⁠It's 4:30 am. means it's 4:30 in the morning, whereas ⁠It's 4:30 pm. means that it is 4:30 in the afternoon.