A monthly index released by the Institute of Supply Management which tracks the amount of manufacturing activity that occurred in the previous month. This data is considered a very important and trusted economic measure. If the index has a value below 50, due to a decrease in activity, it tends to indicate an economic recession, especially if the trend continues over several months. A value substantially above 50 likely indicates a time of economic growth. The values for the index can be between 0 and 100.