A conventional deadlift starts on the floor and you pull from the floor. You end each rep on the floor with a stop. Then, pull again.
A RDL begins standing, with the bar hanging in front of you. You bend forward, sticking your rear out, keeping the bar close to your leg, and lower it until you feel the pull in your hamstrings. You don't go to the floor. Then, straighten. Your back needs to stay in its natural arch and not round. Bend forward again, etc.
Completely different movements.
ETA: See this link:
difference between romanian DL and regular DL