What makes a servo motor a servo motor?

Is a servo motor simply a DC motor with an encoder or tach? Or is there something about the motor itself that makes it a "servo motor"?
Thanks, Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks, everyone. Very informative - I learned a lot. Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.