The Japanese Core 4000 covers the 4th 1,000 most commonly used words in Japanese.
We recommend you first read our Guide to Japanese. This will explain the basics of inputting Japanese.
The Core 4000 is suitable for upper-intermediate students of Japanese. Mastering all 4,000 items and sentences of the Japanese Core 1000, 2000, 3000, and 4000 will allow you to function independently in most contexts.