An adverb used with negative sentences meaning 'not particularly', 'not especially', or 'not very'. It can be used in both spoken and written Japanese but has a slightly formal tone.
彼の説明はさして分かりにくいものではなかった。
His explanation was not particularly hard to understand.
その事件はさして大きな影響を与えなかった。
That incident did not have a significant impact.
さして問題はないと思いますよ。
I don't think it's much of a problem.