What classifies a strip as a "second"

When the factory has a production run, the strips must go through quality control. Some strips will have very minor imperfections such as tiny fingernail type scratches or the end isn't cut quite straight or in laying the glue, for the back of the strip, it may have not been applied straight. Whatever the imperfection, it is never of a nature that would harm the stamp or impair the display of the stamp. In most instances, you will not even be able to see the imperfection.