The word "at" is a preposition used to indicate a specific location or point in time. For example, you might say, "I am at the park" to show where you are. It helps to clarify the position of something in relation to other objects or places. Additionally, "at" can denote a particular moment, such as in the phrase, "The meeting starts at 3 PM." This usage helps to specify when an event will occur, making it clear for everyone involved.