How are hours referred to in English and what are some common expressions used to indicate time?

n English, hours are typically referred to using the 12-hour clock system. The common expressions used to indicate time include:

1. "AM" and "PM": AM stands for Ante Meridiem (before noon), and PM stands for Post Meridiem (after noon). These are used to differentiate between morning and afternoon/evening hours. For example, 9:00 AM and 9:00 PM.
2. "o'clock": This is used to indicate the exact hour without specifying minutes. For example, 3 o'clock, 7 o'clock.
3. "quarter past" and "quarter to": These expressions are used to indicate 15 minutes past the hour and 15 minutes before the next hour, respectively. For example, 4:15 is "quarter past four," and 5:45 is "quarter to six."
4. "half past": This expression is used to indicate 30 minutes past the hour. For example, 2:30 is "half past two."
5. "minutes past" and "minutes to": These expressions are used to indicate the number of minutes past or before the hour. For example, 10:05 is "five minutes past ten," and 6:55 is "five minutes to seven."
6. "in the morning/afternoon/evening/night": These expressions are used to indicate the general time of day. For example, 10:00 in the morning, 3:30 in the afternoon, 8:45 in the evening, and 2:00 at night.

It's important to note that in formal or professional settings, it is common to use the 24-hour clock system, where the hours are represented from 00:00 to 23:59.