The Oxford Advanced English-Chinese Dictionary 9th Edition is a free education and reference app developed by Wanyouzhidian Digital Media Technology Co. Ltd. for the iPhone platform. This app is a mobile version of the world-renowned Oxford Advanced Learner's Dictionary, which has been in existence for over 70 years, and has sold over 100 million copies worldwide. The app contains over 185,000 words, phrases, and meanings, including the Oxford 3000 core vocabulary and academic words, and provides clear and concise definitions and grammar patterns. The app also features illustrations and thematic images to aid in understanding, making it a useful tool for those learning English.

The app has undergone over 6,000 revisions and updates, with over 700 new words and meanings added since the 8th edition. The 9th edition also includes exclusive content not found in the print version, such as contextualized language usage explanations. The app is supported by Shanghai Haide Digital Publishing Technology and its subsidiary, providing customer and technical support. However, it should be noted that the app offers a subscription service, which may not be desirable for all users.