Siamese means 'As Couples or
That is, those who are a Couple work As Couples, and the others
work In Tandem to do the given call.
Sometimes it is difficult to determine who is paired with whom within the
Siamese unit. From a 1/4 Box (see the left-most diagram below),
are often tricked into thinking they are part of a Tandem unit when
in fact they are part of an As Couples unit.
Also, the dancers
are often tricked into thinking they are working in a Tandem
unit with dancers
As Couples CONCEPT [A1]:
Dancers side-by-side and facing the same direction (i.e., a Couple)
work as a single dancer to do the given call.
See also Tandem CONCEPT [C1]
and Solid CONCEPT [C2].