What is the meaning of "axis" attribute in a Pandas DataFrame?

Question

Taking the following example:

>>> df1 = pd.DataFrame({"x":[1, 2, 3, 4, 5], 
                        "y":[3, 4, 5, 6, 7]}, 
                      index=['a', 'b', 'c', 'd', 'e'])

>>> df2 = pd.DataFrame({"y":[1, 3, 5, 7, 9], 
                        "z":[9, 8, 7, 6, 5]}, 
                      index=['b', 'c', 'd', 'e', 'f'])

>>> pd.concat([df1, df2], join='inner')

The output is:

   y
a  3
b  4
c  5
d  6
e  7
b  1
c  3
d  5
e  7
f  9

Since axis=0 is the columns, I think tha concat() only considers columns that are found in both dataframes. But the acutal output considers rows that are found in both dataframes.

What is the exactly meaning of axis parameter?

Answer 1

If someone needs visual description, here is the image: