Order error tolerance

What is the meaning of Order error tolerance in AR setup form ?

Thanks in advance

which version? which tab?

AX 2009 or 2012 - > AR Parameters - > Summary update tab

Select the type of message to be displayed when orders are summary-updated and do not match the criteria set in the Summary update parameters form:

Seems pretty straight forward from the help - basically you are summary update, the batch criteria contains elements it cannot summarize by and this is how you handle those.