Smooth (of a surface): having no roughness or bumps; pleasant to the touch.
このクリームを使うと肌が滑らかになる。
Using this cream makes your skin smooth.
ガラスの表面はとても滑らかで反射が美しい。
The glass surface is very smooth and the reflections are beautiful.
このチョコは口どけが滑らかだ。
This chocolate has a smooth melt-in-the-mouth texture.
Smooth (of action or proceedings): fluent, effortless, or trouble-free (e.g., speech, negotiations).
彼のプレゼンは滑らかで聴衆を引きつけた。
His presentation was smooth and captivated the audience.
交渉は予想より滑らかに進んだ。
The negotiations progressed more smoothly than expected.
彼女は滑らかな英語を話すので会議でも頼りになる。
She speaks fluent English, so she's reliable in meetings.
In mathematics: continuously differentiable; a function that is smooth in the technical sense.
この関数は二回連続で微分可能で、滑らかであると言える。
This function is twice continuously differentiable and can be called smooth.
曲線が滑らかであるため、接線の性質を調べやすい。
Because the curve is smooth, it's easy to study the properties of its tangent lines.