The correct answer is "The software used to produce documents, such as letters, posters, reports, and syllabi." This answer accurately describes what a word processor is. A word processor is a software application that allows users to create, edit, and format text-based documents. It provides tools and features for typing, formatting, and organizing text, making it suitable for producing various types of documents such as letters, posters, reports, and syllabi. The other options mentioned in the question, such as typing a letter using an Excel document, processing information using a number keypad, or working as a database directly from the hard drive, do not accurately define what a word processor is.