Fundamentally, there is a difference between surface-mount technology (SMT) and surface-mount device (SMD). It is because one is a process, whereas the other is a device.
SMT is the method of placing components (like an SMD) on the board. Here, a calculated amount of solder paste is applied to the board. Then, the pick-and-place machine is used to mount the SMD component onto the board.
An SMD is an electronic component that can be found on a Printed Circuit Board (PCB). It is designed to be mounted directly on PCB.
Through-hole-technology (THT) involves inserting leads of components into drilled holes in the PCB. Leads can then be soldered onto pads or lands on the solder side of the board, usually with a simple soldering iron by hand or wave soldering process. Soldering a Dual-in-line package (DIP) IC on the PCB is an example of THT.