The phrase "deep slump" refers to a severe and long-lasting economic decline or downturn. It means that the economy is doing very poorly, with high levels of unemployment, low production, and widespread financial struggles. Full definition
Since 2011 commodity prices in general have gone into a deep slump, with last year's oil crash crippling the energy sector. (canadianbusiness.com)
This effort significantly boosted overall GDP growth and «pushed the Chinese economy out of a deep slump,» says research firm BCA Research. (usfunds.com)
Recessions spawn economic nationalism, protectionism, and the deeper the slump, the stronger are those tendencies. (mauldineconomics.com)