What is congenital abnormality of L1 transverse process?

Back deformity. It's an abnormality of the vertebra at the upper part of your lumbar region (low-mid back). The arm of the vertebra that goes off to the side is not normal. You were born with this, thus the word congenital. It may or may not cause any problems. Talk with a back specialist (spine orthopedic surgeon) if having problems with your back.