数日 (sūjitsu) means “a few days” | MotiTan Japanese Dictionary

More examples

その荷物が届くまで数日かかります。so no ni motsu ga todo ku ma de sū jitsu ka ka ri ma su

It will take a few days for the package to arrive.

Expresses a small number of consecutive days as one short period.

数日間sūjitsukan: A continuous period extending over several days.
三日mikka: Exactly three consecutive days treated as one period.

多くない日数からなる短い期間。ō ku na i nis sū ka ra na ru mijika i ki kan

The compound 数日 (sūjitsu) consists of 数 (sū, "several") and 日 (jitsu, "day"), giving it the sense of several days.

In everyday scheduling, 数日 (sūjitsu) sounds less exact than 三日 (mikka), so it fits plans whose timing may shift.