When you have a bit of a belly, and you could be easily mistaken for someone who is 2 months pregnant. Therefore, you have a "Two-Month Bump". This doesn't necessarily make a person 'fat', its just a little extra baggage in the tummy area.
*Looking at a photo on Facebook*
Jayne: Oh Lord, I totally have a two-month bump in this picture!
Anacaonia: Oh my goodness! You really do!