Much of Wednesday's trading is being driven by a surprisingly strong reading for August of the U.S. Institute for Supply Management's manufacturing index. So what is it?
The ISM conducts monthly surveys of more than 300 manufacturing firms, focusing on five key areas: employment, production, new orders, supplier deliveries and inventories.
The result is a window into the nation's factories and a read on manufacturing conditions. A number above 50 indicates that the sector is expanding.
Wednesday's unexpectedly strong score of 56.3, up from 55.5 in July, is a solid result and offers some much-needed positive news for the economy, according to the analytics firm Econoday Inc.
But Econoday notes that there was still some concerning information in the result.
"Lagging factors gave what is a bit of a deceptive boost to the ISM's manufacturing index masking a further slowing in the key leading index of new orders," the firm said in a report on its site.
Specifically, new orders slowed to there lowest point since the recovery in manufacturing began in the second quarter of 2009.