5 x 5 would mean 5 feet tall with a diameter of 5 feet, but... Such measurements are a rough guide only as to what to expect after ten years of growth. The shape of the plant would depend on many factors, especially the direction from which the strongest light comes.

Yes.......plants rarely grow in a perfect circle :-) Something I need to explain to my design clients often, as they look at a design plan with perfectly round symbols indicating the plants! We can't predict Mother Nature but quoting sizes as a uniform diameter and drawing plants only as as circles is about as close as we can come to guestimating how much space they will occupy.

And just as an fyi, a quick crash course in plant geometry is that the circumference (the distance around a circle or the canopy/dripline of a plant) will never be the same as the width or the diameter across the canopy (C= 2 pi x r {r=radius}). For spacing needs, we assume the trunk will be in the center of the plant and use half the spread - or the radius of the circle - as our guide.