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 exact place or moment being referred to in a sentence. Additionally, "at" can express a particular activity or event. For instance, "She is good at math" indicates proficiency in that subject. This usage highlights a skill or focus related to a specific area or task.