In linguistics, the plain or direct style (non-polite) — using dictionary/plain forms rather than polite 'desu/masu' forms; contrasted with the polite style (keitai).
小説の一人称語りでは常体がよく使われる。
First-person narration in novels often uses the plain style.
敬体（〜です・〜ます）と常体（〜だ・辞書形）の使い分けは日本語学習で重要だ。
Distinguishing between the polite style (desu/masu) and the plain style (da/dictionary form) is important for studying Japanese.
教師は学生に常体で日記を書かせ、文法の確認をした。
The teacher had students write diaries in the plain style to check their grammar.