terminology - Is the bottom of a box does not have a part that tuck in to seal the box still called a flap?

per this answer

The bits at the top and the bottom that tuck in to seal the box are called the flaps.

apparently the top (labeled blue) of the box shown below is a flap.

while the bottom (labeled red) of the box does not have that kind of things, is it still called a flap?