Read while write operation refer to the boot loader operation.
Well,
the ATmega32 has a 32k flash memory. This memory is organized in two main sections, the Application section and the Boot Loader section, and the size of the different sections is configured by some fuse bits called BOOTSZ Fuses.
The Application section is the section of the Flash that is used for storing the application code.
The boot loader section is a section of Flash that u can place a code (called boot loader software) that can be copied (this called self program) to the application section to be executed under some constraints.
This operation (self programming or writing) cane be done while the application code is executed (or read) >>>>>>>>>>> that is called <<<Read While Write>>>