Glue logic is digital logic used to connect various devices on Printed Circuit Boards. It may be implemented with 74 series logic or programmable logic devices, such as CPLDs or FPGAs.
The name comes from the fact that this digital logic is the glue that holds together all of the interconnects on the board.
Glue logic is very helpful for designers, as it helps the designer integrate several devices with different logic voltage levels. When using a CPLD or a FPGA, glue logic is reconfigurable, allowing the easy change of hardware and i/o connectivity in the future