Debossing is a process for making an indented image in a material, using a metal die. There is no ink involved in this process, and the die used will also create the debossed design as a reverse embossed (raised) design on the other side of the card.
Letterpress is a printing process with the main purpose of adding ink - Letterpress was not designed with the purpose of making an indent, however this is a result of the process. We offer blind letterpress, which is the same process as letterpress just without using any ink - this is offered as an option to create an impression on one side of the cardstock without affecting the other side of paper like the debossing method will.
This blind letterpress process is not the same as traditional debossing and will have a bit more subtle effect, as debossing will create a much deeper indentation than letterpress. Blind letterpress is useful for one ply orders since it will not show an emboss on the opposite side.