Im was currently develop a new bootloader for PIC16F877A instead of
PIC16F877-20P to be used with GoGo Board.

Since there are changes in the self-programming mechanism for Flash
program memory, where on PIC16F877 devices, Flash programming was done
in single-word erase/write cycles while the newer PIC16F877A devices
use a four-word erase/write cycle.

What is the meaning of single-word erase/write cycle and four-word
erase/write cycle?

Any one know how to modify the PIC16F877 bootloader so that it can be
used for PIC16F877A?