Mint stamps, cancelled by postal authorities without having been used for postage. Have a postal cancellation, but with glue. Mostly of used Russian stamps in 1962-2001 is a CTO, (Also East European, African)
Canceled To Order. Stamps are "canceled to order," usually in full sheets, by many governments. Often, the cancels are printed on the stamps at the same time that the stamp design is printed. CTO stamps are sold to stamp dealers at large discounts from face value. CTO stamps have never seen actual postal use. Most catalogues say whether they price CTO stamps or genuinely used ones. A stamp with a cancel and with full gum is likely a CTO stamp.
stamps cancelled to order, but not used postally