PMI (Purchasing Managers' Index)
The PMI is an index built from surveys of purchasing managers. Above 50, activity is expanding; below 50, it is contracting.
PMIs survey companies each month on orders, output, employment, delivery times and prices. They exist for manufacturing and services and are published by S&P Global for many countries. In the US, the ISM publishes comparable indices.
Their strength is speed: flash estimates come out before the end of the month in question, well ahead of GDP. They are leading indicators of the business cycle.
The market looks at the level relative to 50, the gap with consensus and the sub-components, such as prices paid, which hint at future inflation. A reading above or below 50 matters most when it marks a change from the previous month.