At is a preposition which is commonly used to indicate a specific point in space, time or within a range. It is used to describe a particular location, position or event. For instance, "at" can be used to describe the location of a person waiting at the bus stop, the time for a meeting scheduled to start at 3:00 PM, or the event of meeting each other at a concert. The usage of "at" helps provide context and clarity about where, when, or within what boundaries something is happening. Therefore, it is an important preposition that is frequently used in day-to-day communication.