Output represents the value of industry production. In IMPLAN these are annual production estimates for the year of the data set and are in producer prices. For manufacturers this would be sales plus/minus change in inventory. For service sectors production = sales. For Retail and Wholesale trade, Output = gross margin (or Marginal Revenue) and not gross sales (Total Revenue), which includes the value of the goods sold.
For industries that do not hold inventory, output equals revenues (sales). For industries that do hold inventory, output equals revenues less any net change in inventory (additions to inventory less sales out of inventory); for these industries, it is possible for a year’s sales to exceed that year’s value of production, if some of those sales came out of inventory (a previous year’s production); in I-O models, what matters is the value of production that occurred in a year, since production is what drives the purchases of inputs. Sales of items that have been sitting in inventory do not generate indirect and induced impacts this year since they were produced in a previous year; thus, we don’t want to count them as part of this year’s output, else we’d overstate the indirect and induced impacts.
IMPLAN defines Total Industry Output as the Value of Production or Labor Income + Intermediate Expenditures + Tax on Production and Imports + Other Property Income. For detailed information about Output and its components visit Understanding Output (O).