Transpose[list]square = {{1, 2, 3}, {4, 5, 6}}; Transpose[square]
MatrixForm[%]
matrix = {{1, 2}, {3, 4}, {5, 6}}; MatrixForm[Transpose[matrix]]
matrix3D = {{{1, 2}, {3, 4}}, {{5, 6}, {7, 8}}}; Transpose[matrix3D]
Transpose is its own inverse. Transposing a matrix twice will give you back the same thing you started out with:
Transpose[Transpose[matrix]] == matrix
Transpose[Transpose[matrix3D]] == matrix3D
If the rank of the list is 0 or 1, you get the list back
Transpose[{}]
Transpose[{a, b, c}]