"at C6/7 left lateral recess disc herniation flattens the cord causing potential exiting left C7 nerve root impingement."
The lateral recess is an area, sort of like a groove, where the nerve root exits the spinal canal. There is a lateral recess on each side of the vertebra. After traveling through the recess the nerve root goes through the neural foramina to finally exit the spine. The word foramina just means hole.
So, on the left side, at the C6-7 disc, there is a herniation that sits in the lateral recess pressing up against the thecal sac (the covering of the spinal cord) causing the usually rounded edge of the spinal cord to be flattened.
The radiologist also thinks that the C7 nerve root might have some pressure on it, as it travels through the lateral recess. He/she can't be sure, but where the herniation is, there is the possibility that it could be, so it is stated as having the potential for impingement.
You need to discuss the findings with your physician. The study will have to be correlated with your history, symptoms, and physical exam.