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notches; serration; indentation; jaggies (stair-step artifacts in computer images)
notched; serrated; jagged; corrugated; milled
「段段」 has another reading with different meanings.
岩が段段で手を切った。
The rock was jagged and I cut my hand.
はさみでぎざぎざに切ってみた。
I tried cutting it jagged with scissors.
段段の模様を描いてみた。
I tried drawing a jagged pattern.