What is meant with a buffer in python

Question

In the python documentation for struct, the word buffer is used without explanation:

http://docs.python.org/library/struct.html

struct.unpack_from(fmt, buffer[,offset=0])

Unpack the buffer in accordance with this format. the result is a tuple, even if it contains exactly one item. The buffer must contain at least the amount of data required by the format (len (buffer [offset:]) must be at least calcsize (FMT)).

What is meant here with the buffer. Is the string a buffer or file descriptor? What methods should have a "buffer"?

Answer 1

: Python 2, (str), Python 3, (bytes) , , , buffer.