length - length of object
For usual or polynomial matrix n is the integer equal to number of rows times number of columns of M. (Also valid for M a boolean matrix)
For matrices made of character strings (and in particular for a character string) length returns in n the length of entries of the matrix of character strings M.
The length of a list is the number of elements in the list (also given by size).
length('123') is 3. length([1,2;3,4]) is 4.