The short answer is Solo and Main.referring to 2 of the pipe chambers generally found in a theatre pipe organ installation. In addition, in some larger TPO installations, there is a String Chamber such as referenced here
http://alabamatheatre.com/about-the-alabama/the-mighty-wurlitzer
A virtual tour of the Main Pipe Chamber here:
http://alabamatheatreorgan.com/Main.html
A virtual tour of the Solo chamber here:
http://alabamatheatreorgan.com/Solo.html
The "names" of these pipe chambers gives an idea of the particular pipe ranks (and percussions) found in a given chamber. If you want to do some further research, check out this reference:
http://en.wikipedia.org/wiki/Theatre_organ
Rgds,
Ed