1.
inner feelings, inner self, psychological interior
A person's inner thoughts, emotions, and psychological state, as opposed to their outward appearance or behavior.
内面を磨く。
Cultivate one's inner self.
外見だけでなく内面も大切だ。
Not just appearance but inner qualities are also important.
この小説は主人公の内面を深く描いている。
This novel deeply portrays the protagonist's inner world.
2.
inner surface, inside
The interior surface or inside of a physical object.
パイプの内面を清掃する。
Clean the inner surface of the pipe.
壁の内面に断熱材を入れる。
Insert insulation material on the inner surface of the wall.
ヘルメットの内面にクッションが付いている。
There is cushioning on the inside of the helmet.
Sense 1 is far more common in everyday usage. Often contrasted with 外見 (outward appearance) or 外面 (exterior).
COMMON COLLOCATIONS:
- 内面を磨く (polish one's inner self, cultivate character)
- 内面の美しさ (inner beauty)
- 内面的 (internal, psychological)
- 内面描写 (depiction of inner feelings)
DISTINCTIONS:
- 内面: inner side / inner self (broad — physical or psychological)
- 内心: one's true feelings (always psychological, often hidden)
- 外面: exterior, outward appearance