An inspection is a review to confirm the quality of a product. Inspections vary widely in their formality, and in the location where they are done.
The closer an inspection is to the point where an error is made, the quicker the problem can be corrected.
Inspections may cover 100% of a product when extremely high quality is required (normally for a high risk product or service), or when processes are not well-developed.
Sampling is a way of inspecting part of a population of products (or services) and making a judgment about the overall quality. It is less costly than 100% inspections, but more prone to letting poor quality escape.
In any form, though, inspections are waste. It is much better to use Lean methods to build quality into a product than to try to inspect it in later. This is often accomplished using using poka yokes.