The Romanian Deadlift originated as an assistance exercise in developing strength for Olympic Weightlifting and owes its name to Olympic champion Nicu Vlad of Romania who first demonstrated the exercise in the USA. It can be described as a combination of a stiff-leg deadlift and a normal deadlift, but it is in fact neither.

Essentially it is what we would call a hip hinge pattern which requires effective control of spinal alignment and stabilisation of lumbar spine and pelvis. Developing a strong, well-controlled hip hinge pattern is essential for progress to heavier lifting and for protecting the back in everyday lifting activities. Failure to execute a successful hip hinge strategy during lifting or movements that load the spine can be a key contributing factor in developing lower back pain.
Perhaps most important about the movement is that it emphasises eccentric control of the movement by the hamstrings and glutes. The weight is lowered slowly from the standing position as the hips fold and the back remains aligned in a natural curve (neutral alignment).

An eccentric muscle contraction is one which decelerates movement due to the force of gravity. What we tend to think about when considering a muscle contraction is a concentric contraction where muscle fibres shorten in length as we lift a weight up against gravity. In an eccentric contraction, however, we move in the direction of gravity lowering the weight slowly resisting the pull of gravity as the muscle fibres lengthen under loading.

This eccentric strength is extremely important for function and performance as normal human movement is a combination of concentric, eccentric and isometric (muscle fibres remain at same length) contractions. Our hamstrings need to demonstrate strength in each contraction type for walking and running and the relative importance of each is the subject of much current research.