通俗 (tōng sú): common; everyday; average

This history book tells complex events in plain language; even middle school students can easily understand it.

The doctor wrote a plain health guide to remind elderly people how to prevent common diseases.

He speaks in a very plain way and never uses technical terms, so everyone enjoys listening to him explain scientific knowledge.

This novel has plain content and vivid characters, making it very suitable for beginners to read.