“Ex” is Latin for without. Ex-interest means “without interest”. An interest rate quotation norm that is used in quoting prices of government securities and debentures. It means that the security is quoted exclusive of interest.

Payment to seller = quotation price + accrued interest

The accrued interest is not part of the quotation price.

In that sense, ex-interest only covers the cost of the security in question, and the buyer will be required to pay an additional amount (the accrued interest) over the cost up till the date of purchase.