About two or three days; a short period of a few days.
体調が悪いので二三日休みます。
I'm feeling unwell, so I'll take a couple of days off.
荷物は二三日で届くはずだ。
The package should arrive in two or three days.
二三日後に連絡しますのでお待ちください。
I'll contact you in two or three days, so please wait.