Find the least significant digit of 2^3*A where A=10^100

Find the least significant digit of 2^3*A where A=10^100

I am a n00b.. Can anyone please tell me -
What is the least significant digit in the Q above?
How do we define least significant digit?
All I know is that since we can represent the above number as 8*10^100..
the least significant digit is 8 (i i am not sure)..