D&D 5E doesn't have back stabbing anymore. They have what is called Sneak Attack. The following is from the D&D 5E SRD.
SNEAK ATTACK
Beginning at 1st levei, you know how to strike subtly
and exploit a foe's distraction. Once per turn, you can
deal an extra Id6 damage to one creature you hit with
an attack if you have advantage on the attack rol!. The
attack must use a finesse or a ranged weapon.
You don't need advantage on the attack roll if another
enemy of the target is within 5 feet of it, that enemy
isn't incapacitated, and you don't have disadvantage on
the attack rol!.
The amount of the extra damage increases as you
gain leveis in this class, as shown in the Sneak Attack
column of the Rogue table.
So while the position of the rogue in not of concern to get a sneak attack, and can even be a ranged weapon. The position of others in your party can contribute to whether you get a sneak attack.
