The polite speech/writing style that uses masu/desu endings to show politeness; often contrasted with plain style (da/plain form).
面接では丁寧体で話すのが基本だ。
In interviews it's standard to speak in the polite style.
日本語の教科書は初級では丁寧体を中心に教えることが多い。
Textbooks often teach the polite style as the focus in beginner Japanese.
友達には普通体、目上の人には丁寧体を使い分ける。
You use plain form with friends and the polite form with superiors.