Leonard & Peggy Brown wrote:
I am not new to bicycles. I was a pretty active rider back in the
70s but
lost touch with things over the last 30 years. I have seen several
references to "machine built wheels". What does that mean? I can't
really
see a machine clever enough to just put steel parts in one end and
wheels
come out of the other. Please enlighten me.

The issue with "machine built" wheels is that they're generally
delivered under-tensioned. Riding wheels like that often causes spokes
to go slack enough to unscrew nipples as they are loaded by the rider's
weight. It's not uncommon to find rattling-loose spokes after a ride or
two.

Machine-built wheels can be fine if they're brought up to ideal tension
and stress relieved (see bike FAQ &/or articles on Sheldon Brown's
site).