The Second Extended File System (ext2 or ext2fs) is a Linux file system that was popular in the 1990s. It had a reputation as a reliable file system, but it is not widely used anymore, since it lacks some advanced file system features, such as journaling.
ext2 is still sometimes used for small partitions, e.g. for a boot partition. On small partitions, the size of the journal used by more advanced file systems can be a problem, so ext2 is a logical choice. It supports files of up to 2 TB, filesystems of up to 16 TB, and filenames of up to 255 characters.