Bush / tree difference?

Question

What is the difference between a bush and a tree?

Like, the classification system?

Answer 1

Generally the difference is based on the mature height of the plant.  For example, crape myrtles can grow miniature, dwarf, bush, or tree sized.  Miniatures are very short plants with each of the others taller in height!

Answer 2

Actually, the difference is the multiplicity of stems at the base and the diameter to which any stem can potentially grow at 4.5 feet above the ground (what's considered breast-height, as in the term diameter at breast height, or dbh).  Trees generally grow as a single stem, but shrubs have numerous stems where they emerge from the ground.  That's how shrubs can be differentiated from young trees which may be close to the same height.  But when mature, trees have the capability of having diameters over 3 inches at this height where because of their branching habit, shrubs don't.