HSN stands for Harmonized System of Nomenclature. It is a system for classifying commodities created by the World Customs organization. U.S. LTL shipping, however, uses NMFC classifications instead.
Freight Class 500 freight is the most expensive to ship. This classification is reserved for items of very high value or for items that use lots of space but weigh very little.
NOI stands for Not Otherwise Indicated. This is used when a commodity does not have an NMFC code. In these cases, density is usually used to determine freight class.