To write an essay means to compose a written piece that expresses an opinion or discusses a topic, usually in response to a prompt or question. It involves using organized thoughts, supporting evidence and examples to convey a message or argument in a clear and concise manner. Essays can be formal or informal, and may take on various forms such as descriptive, narrative or persuasive. The goal of writing an essay is to present a well-thought out and coherent piece of writing that demonstrates the writer's ability to research, analyze and express their ideas effectively.