Here is a long but understandable explanation:
The stock market fell sharply on Friday due to renewed recession fears. Major news and data reports caused investors to worry the economy could be headed for a recession.
AIG reported a record $5.3 billion loss due to huge writedowns from bad mortgage investments. Their shares dropped 7%. Dell also missed earnings targets and warned of weak customer spending, dropping their stock 1.5%. Reports said a bailout of bond insurer Ambac was facing problems, sending their stock down 7.5%.
Economic data also fueled recession concerns. A report on Midwest manufacturing fell more than expected to a six-year low, indicating weakness in that sector. Consumer sentiment declined to its lowest