Wiktionary is a free online dictionary that provides definitions, pronunciations, and translations for words in multiple languages. It is a collaborative project, allowing users to contribute and edit entries, ensuring that the information is constantly updated and expanded. As a sister project of Wikipedia, Wiktionary aims to create a comprehensive resource for language learners, linguists, and anyone interested in words. It includes not only standard definitions but also etymologies, usage examples, and grammatical information, making it a valuable tool for understanding language.