To stand on tiptoe, lifting the heels so only the toes support the weight.
棚の上の箱が見えなくて、思わず爪先立って覗き込んだ。
I couldn't see the box on the top shelf, so I instinctively stood on tiptoe to look.
子どもが観客の背で見えないから、爪先立って舞台を見ていた。
The child couldn't see over the audience, so they stood on tiptoe to watch the stage.
バレエの基礎では、まず爪先立つ練習から始めることが多い。
In ballet basics, practice often begins with standing on tiptoe.