count and Len difference in Pandas

In [6]: import pandas as pd

In [7]: import numpy as np

In [8]: s = pd.Series(['a','b','c','d',np.nan])

In [9]: s.describe()

Out[9]: 

count     4

unique    4

top       c

freq      1

dtype: object

In [10]: s

Out[10]: 

0      a

1      b

2      c

3      d

4    NaN

dtype: object

In [12]: s.count(),len(s)

Out[12]: (4, 5)