Ext2 is the Extended Filesystem, version 2. It grew out of the MinixFS, which had some very strict limitations.
Ext2 used to be the default FileSystem for almost every Linux box for many many years. It is rock-solid and has an excellent fsck(8) which can recover from most situations. Very little data has been lost from Ext2 partitions, even though it has no journalling support. Another problem is that its directory handling doesn't scale well to large directories.
Therefore, with growing HardDisk capactites its new successor Ext3 with journalling support has become popular.
See also:
Linux