In a commercial/industry sense one handed soldering is referenced as a technique in which the individual "carries" solder with his/her iron from the spool over to the point of contact. Meaning he does not utilize his second hand to add solder.
This is usually acceptable for most commercial applications. Although there are instances where it is deemed unacceptable because the level of reliability at the joint may not meet the standards of a certain governing body. Certain aerospace standards come to mind.
Thanks
Blake