Microsecond (µs)
Definition: A microsecond is one millionth of a second.
History/origin: Microseconds became widely used once electrical engineering, audio systems, and computing required more precise timing than milliseconds.
Current use: Microseconds are used in embedded systems, sensors, audio processing, robotics, and data transmission timing.
Week (wk)
Definition: The week is a calendar interval of seven days, commonly used to group work, school, religious, and planning cycles.
History/origin: Seven-day cycles spread through ancient religious, astronomical, and civic traditions before becoming embedded in modern international calendars.
Current use: Wk is common in work schedules, class plans, sprint planning, pregnancy tracking, subscriptions, recurring chores, rent cycles, and short-term goals.