M4A files, for example, are generally smaller in size and can store audio in better quality than MP3s.
MP4 (also known as MPEG-4) is in turn based on QuickTime File Format (QTFF) and, in some sense, was developed to replace MP3. You might be more familiar with M4A files if you think of them as MP4s, which they essentially are - the only difference is that an MP4 file can handle video while.
