In a process we have two section bss and data, global and static variables are stored in the data segment, and uninitialized data are in the bss segment.
The .bss segment is an optimization. The entire .bss segment is described by a single number, probably 4 bytes or 8 bytes, that gives its size in the running process, whereas the .data section is as big as the sum of sizes of the initialized variables. Thus, the .bss makes the executables smaller and quicker to load.
I hope this clarifies the doubt.