It also involves developing standard testing procedures and materials. The result should be a test that reliably measures the same thing the same way each time, so that scores are comparable. A standardized test should also demonstrate validity, meaning that it actually measures what it portends to measure. A test score should correlate with something in the real world. Norming is the process of determing average scores for average people.
Norms are important because they help give test scores meaning - something to compare to.
A raw score of 7, for example doesn't mean much. It means more to know that a score is at the 50th percentile for an individual of a certain age. This permits test scores to be compared to average, to each other on a relative basis, or to scores on other normed tests. The three major types of norm scores are age scores, percentiles, and standard scores. Tests can be normed on more narrowly defined populations, although the usefulness of these scores varies with the definition of the norm group.