Here, “maskable” means "prohibited.“
When an interrupt request signal occurrs, the interrupt processing can be performed if the CPU is set to enable the interrupt.
If the interrupt is set to disable, the interrupt request signal is ignored and the interrupt processing is not performed.
The ignored interrupt request signal is retained until the interrupt request changes to enable or the command is cancelled by the program.
In this way, the maskable interrupt can enable or disable the interrupt processing freely.
It is usually set by the program.
The CPU receives the interrupt request signal, and the interrupt control circuit shifts to the interrupt processing operation.