NameError: name 'pd' is not defined
Select Restart & Clear Output and run the cells again from the beginning.
I had the same issue, and as Ivan suggested in the comment, this resolved it.
If you came here from a duplicate, notice also that your code needs to contain
import pandas as pd
in the first place. If you are using a notebook like Jupyter and it's already there, or if you just added it, you probably need to re-evaluate the cell, as suggested in the currently top-voted answer by martin-martin.