1An onomatopoeic adjectival word describing something full of gaps or holes, spongy/porous, or content that is thin/insubstantial.
このパンは中がスカスカで、あまり美味しくない。
This bread is airy/empty inside and not very tasty.
彼の説明はスカスカで、具体性が欠けている。
His explanation is thin and lacks specifics.
古い靴下は生地がすり切れてスカスカになった。
The old socks have worn thin and become threadbare.
2An onomatopoeic adverb expressing something being cut or entering sharply/cleanly (similar to 'with a clean cut' or 'neatly').
包丁がよく研がれていて、野菜がスカスカと切れる。
The knife is well sharpened and cuts vegetables cleanly.
3A rare/archaic adverbial sense meaning 'to progress smoothly' without hindrance.
工事は思ったよりスカスカと進んだ。
The construction progressed more smoothly than expected.