What is the US, Russia ‘deconfliction line?’

A communication link between U.S. and Russian military officials has protected pilots flying missions over the crowded skies of war-ravaged Syria, but now Moscow says it is suspending its cooperation over an American missile strike.
The following is an explanation of the so-called “deconfliction line” and the possible consequences of cutting it.
___
Flying the unfriendly skies
A U.S.-led coalition has been bombing Islamic State-held territory across Syria, launching 24 strikes on Thu