Final answer:
A dictionary is a practical, user-friendly reference that is often available for free online and helps in understanding word definitions and usage.
Step-by-step explanation:
A practical, user-friendly, and often freely available online reference is a dictionary. Dictionaries such as those found on the internet or as apps for smartphones provide definitions, word histories, syllabication, and guidance on correct spelling and usage. For those seeking to understand words and their proper applications, dictionaries have evolved over time to include new words and omit those that fall out of use, thus keeping up with changes in language. They are essential for reliable communication, offering more than 100 words for definitions and facilitating a precise understanding of language.