A 'Sewer Scope' is a camera that is pushed through the (lateral) drain piping, from the interior stack, to the city sewer main (or private septic tank in the country). It is highly recommended for older (sectioned) cast iron and / or clay tile systems, which most are. Updated PVC stacks (in basement) often transition to cast iron at the basement floor, vs. being PVC all the way out. These older systems can be in perfect condition, and function well, if not with heaving, settling, breakage, or root intrusion anywhere along the pipe. The only way to be sure none of this is happening is by having a Sewer Lateral Scope Inspection performed.
Sewer 'lateral' is the piping from the sewer stack, usually located in the basement, to the main sewer piping (usually) under the street. We often find cast iron, or clay tile while inspecting St Louis and St Charles county homes, for which a sewer lateral 'scope' or 'camera' is highly recommended before closing.
The scope comes with a report from an experienced professional, usually with recommendations of 1 time or regular actions to take, to keep the system in working order.
The report may recommend jetting if there is sediment in a belly or depressed section of the pipe, cabling if there is root intrusion, and/ or regular chemical treatment to kill roots that may be entering the piping at seams. Worse, an offset or collapse in the piping could be found, most often undetectable from above ground, and hard to repair any other way than digging up the piping and replacing it.
PVC piping is less susceptible to intrusion, and newer homes will likely have this type of sewer and storm drain piping. A sewer scope still can be a good idea, to ensure no issues exist underground.