Minimum call notice days is the minimum number of days' notice that a bond issuer must provide to bondholders before calling (redeeming) the bonds prior to their maturity date. This provision is typically outlined in the bond indenture and specifies the minimum advance notice period required for a bond call. 

The purpose of minimum call notice days is to ensure that bondholders have sufficient time to prepare for the early redemption of the bonds and to make informed decisions regarding their investments. 

By providing a minimum call notice period, issuers allow bondholders to consider their options, such as reinvesting the proceeds or adjusting their investment strategies in response to the call. Understanding the minimum call notice days is essential for investors as it allows them to anticipate potential bond redemptions and plan their investment portfolios accordingly.