What makes a front door?

The one closest to the street? The one closest to the porch? The prettiest one? The one closest to the the mailbox? The one easiest to get to? The one the residents use? Well, I've been pondering this weighty question today. We have four doors into our house: 1) One in the back of the house up a flight of stairs. This enters into the kitchen and is the one we use. 2) One below the kitchen door which enters into an enclosed patio in the basement. 3) A door on the side of the house which enters between the main level and the basement. 4) A door on the front of the house which enters into an enclosed porch and then into the living room. I didn't really think which door was the front door when we moved in. I assumed the front door was the one in the front of the house with the mail slot. WRONG!!!! Everyone who has ever been in this house before (which totals three people now) have used the little door on the side of the house. They use the small town greeting of knock quick, open door, poke head inside, and yell hello. My 4yo intrepid explorer is out investigating the rivers on the street. The temps are just above freezing so the mountains of snow are turning into little gushing rivers. My 6yo is trying to avoid falling asleep as she mourns the friends she left behind in Texas. She fell on the steps this morning and launched into a woe-is-me hour begging to go back to Texas. She attends her first RE class tomorrow night, so hopefully we meet a couple nice girls in her class of 5 students. That reminds me to call the school and ask about girl scouts.