To add to js55's reply, consider an AMI, Dimetric Liburdi or Magnatech weld head mounted to a tracking system(pipe, tank or plate doesn't matter). As the weld head travels...YOU can manipulate the arc with the programmer and/or the pendant. Increase/decrease current, amps, oscillation, dwells, travel speed, wire speed, etc. That is considered machine or mechanized welding.
http://www.magnatech-lp.com/Now consider the same name brand systems making autogenous fusion(no wire added) welds on High Purity SS in a Pharmacuetical Plant. After you initiate the arc...the preselected program will complete the weld with no additional arc manipulation from the person. That is an example of automatic welding.
http://www.arcmachines.com/BrochurePDFs_English032502/Model%209%20series.pdfhttp://www.arcmachines.com/Media/M21-series.pdfHope that helps.
Best of my knowledge, when I did Autogenous welding (not all that much) you could not override the program once started=Automatic
With machine welding, you can change something every second or not at all but it is not classified as automatic.