[Python] What does *tuple and **dict mean in Python? [duplicate]

As mentioned in PythonCookbook, * can be added before a tuple. What does * mean here?

Chapter 1.18. Mapping Names to Sequence Elements:

from collections import namedtuple
Stock = namedtuple('Stock', ['name', 'shares', 'price'])
s = Stock(*rec)
# here rec is an ordinary tuple, for example: rec = ('ACME', 100, 123.45)​

In the same section, **dict presents:

from collections import namedtuple
Stock = namedtuple('Stock', ['name', 'shares', 'price', 'date', 'time'])
# Create a prototype instance
stock_prototype = Stock('', 0, 0.0, None, None)
# Function to convert a dictionary to a Stock
def dict_to_stock(s):
return stock_prototype._replace(**s)​

What is **'s function here?

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