It is a 16 bit special function register in the 8085 
microprocessor.It keeps track of the the next memory 
adderess of the instruction that is to be executed once the 
execution of the current instruction is completed.In other 
words, it holds the address of the memory location of the 
next instruction when the current instruction is executed by
the microprocessor.

PC [program counter] is a register holding the address of 
the instruction which needs to be executed next. Its used 
to keep track of current execution point - this tracking is 
necessary for various reasons and some of these reasons are:
1. While branching or looping destination address is 
specified with respect to the current PC value.
2. While branching to a function call current Pc value is 
pushed into the stack and retrieved back when retrunign 
from the function-call. 
3. PC value  is strored when servicing an interrupt and 
restored back after execution of ISR.
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