A sample is a specimen of a product or material set aside for checking, trials or approval. In bag production the word has two separate meanings: specimens taken from the line during production for quality control, and sample bags sent to the buyer for approval before an order.
Properties such as thickness, dimensions, seal seam and print are measured on quality control samples, and the results are recorded. An approval sample, on the other hand, gives the buyer the chance to try the bag under real conditions of use. Filling, carrying and closing the product tells you more than a description on paper. Moving to series production only after sample approval reduces disputes that might arise later.