The difference is intentionally attacking civilians and only civilians. The U.S. military has mistakenly attacked civilians, I assume there have also been cases where there was a high-value target and the deaths of nearby civilians were considered acceptable "collateral damage." (if you want to counter this, please restrict examples to ones since 9/11 and ones when no perpetrators were charged or disciplined).

While the distinctions don't matter to dead people or their surviving loved ones, they do within the oxymoron "military justice."