Dave Lampson, first from Grove:

>   BIS (Fr.), "twice"; (1) a cry equivalent to ENCORE.  The French
>   even have a verb, bisser, to repeat.  (2) When written, as it is
>   sometimes in MS. music, over a phrase or passage, it signifies
>   that the notes are to be repeated; the same thing would be effected
>   by dots of repetition at the beginning and end of the phrase.

These are indeed the first and second meanings of 'bis'.

It has a third meaning.  It can also be used to indicate the repetition
of a number.  It just means a second work assigned a same opus number.
If there were a third, it would be 'ter'.  Houses, for example, can also
be numbered in this way.

>That appears to be a hodge-podge of transcriptions or revisions - sometimes
>right on top of each other (Tchaikovsky); sometimes decades apart (30 years
>separate the Atterberg sonatas) - and just plain ol' doubly assigned opus
>numbers (Rubinstein).

These are the problems that 'bis' and 'ter' neatly solve.

Using a) or b) or actual numbers might seem to indicate that the works
are closely related like the Rasoumovsky Quartets (op.59 Nos 1,2,3) or
Sibelius's "Canzonetta" and "Valse Romantique" (op.  62a, op.  62b), or
that they are recognized transcriptions, or suites from operas or ballets
for instance, as for Martinu's "Spalicek" (H214:  ballet; H214A:  Suite
No1 (Riha); H214B:  Suite No2 (Riha); H214C:  Waltz and Polka for piano)
or Tchaikovsky's "Nutcracker" (ballet:  op.71; suite:  op.  71a)...

'Bis' is from the latin, meaning 'twice', and there's also 'bis repetita'
if you really want to insist;-)

Regards,

Christine Labroche