They became albums when a bunch of 78 rpm records were put together in a booklet in outer appearance much like a photo album. The 78s generally held one song per side. This wasn't sufficient capacity for a piece of classical music, say, Mozart's Requiem, so such a piece of music would have to be put on multiple disks which were stored together in an album. When the technology permitted the capacity of the recording disks to be increased to the point were a large piece of music could be put on one record the term album continued to refer to such a recording.