A dictionary is a reference book that focuses on defining words and phrases, including multiple meanings. The most frequently used dictionary is a language dictionary that includes the majority of frequently used words in a language. Language dictionaries are made for different types of users: scholars, office workers, schools, and second language learners. There are many competing dictionaries put out by different companies. Not only do they have different forms - paperback, hardback, and online editions - but they differ in other ways. Each company, for example, uses its own version of phonetic respelling based on the research done by its experts. Other differences between dictionaries show up in other features. Many dictionaries include their experts' guidance on grammar, usage, and the history of the language. Definitions differ slightly, and sample sentences may be the work of the editorial staff or taken from real-world usage, perhaps the first known written use.