FILESTREAM is a new feature in SQL Server 2008 that enables the storage of unstructured data on a NTFS file system. FILESTREAM (local or remote) is supported in SharePoint 2010 as one mechanism of reducing capital expenditures through enabling the storage of large binary unstructured data on content addressable or commodity storage.

Unstructured Data
Unstructured data refers to information...read more on the SharePoint Team Blog.