Editing is the process of removing unwanted material from a program and piecing together the good sections to create a finished product. For music projects, editing can begin after all recording and mixing is completed. Editing can range from simple removal of "out takes", to rearranging the song order, to precision rearrangement of a musical selection.
In the days of reel-to-reel tape recording, the original mix tape was cut with a razor blade and spliced back together with splicing tape in the proper sequence.
In typical digital editing, the sections of the program are rearranged or deleted in the computer by simply programming the order in which the sound is played back. This is possible because the audio is recorded on a hard disk (random access) rather than on tape. (linear) If something is to be cut out, it is not "erased"- it is simply not "accessed". This is known as "non-destructive editing" because the original recordings are not physically cut or changed.