Bob Atkins , Apr 22, 1999; 10:40 a.m.
The difference is one has an "i", the other has an "a". While technically there might be a difference, most people use the terms interchangably. Lens manufacturers use the terms whenever they want to for marketing reasons. True "macro" or "micro" lenses should go down to 1:2 (1/2 lifesize) or 1:1 (lifesize) reproduction rations. Some 1:4 or even 1:5 lenses have "macro" written on them.
A longer focal length gives you more working distance.