I would guess it's a reference to the port direction bits on a Cypress processor.
"PRT1DR &= 0x7f" means the contents of PRT1DR are ANDed with 0x7F and the result put back in PRT1DR, in other words, bit 7 is made zero with other bits unchanged.
"#define reloff PRT1DR &= 0x7f" just makes a new instruction in your program called 'reloff' which the compiler expands to 'PRT1DR &= 0x7' when it sees it.
So 'reloff' makes bit 7 of PRT1DR become zero.
Generally, we use #define like that to make the program more readable, for example you can use it so a port pin becomes synonymous with what is connected to it. So if you used "#define RelayOn PORTX,6=1" you could use the command "RelayOn" in your code rather than an instruction that didn't describe what it actually did. It also makes it a lot easier to modify the code afterwards. Example: if the relay was changed to bit 5 instead of 6 you only have to change the number in the definition and recompile. Without it you would have to go through the entire code and edit all the occurrences from 6 to 5.
Brian.