Re-partition phone filesystem
Re-Partitioning the internal memory of the phone relocates the available memory from one partition to another. For example, reducing the amount of memory allocated to the internal SD partition and increase the amount allocated to the data partition.
When we flash the ROM, there is the option to repartition using a PIT file. It specifies the sizes allocated to each image file (factoryfs.rfs, modem.bin, etc) in the Flash storage where the ROM is stored. In effect, it is treating the internal storage (not to be confused with the internal SD card) like you would treat a hard drive in a computer. The PIT file just specifies how it's broken up.