What age says
Newborn, four or five naps spread about with little order. At three or four months a rhythm appears and it is usually four. Around six, three. Between nine and fifteen months, two. From eighteen months on, one long nap after lunch.
The brackets are wide on purpose: two babies the same age can take different numbers and both be fine.
And what your baby says
napnap counts the naps of each day once it is closed and learns from that, more slowly than it learns the wake window because this comes in steps and not as an average: half the weight every seven days and forgotten after a month.
Only days with something recorded count. A blank day almost never means they did not sleep: it means nobody tapped the button, and counting it as zero would drag the number down by force.
Why the number matters more than it looks
The shape of the whole day comes out of it. With three naps, the last window is the long one and bedtime falls where it falls; with two, everything stretches.
It also decides when the next thing is the night rather than another nap, which is the difference between warning you at six in the evening about a nap that is no longer due and warning you about bedtime.