At least one: or

The operator or combines two conditions into one that is true when at least one of them is true:

day = input("Day: ")
if day == "Saturday" or day == "Sunday":
    print("No school today!")
else:
    print("Time for school.")

Sunday

Day: Sunday
No school today!

Here are all four combinations:

>>> True or True
True
>>> True or False
True
>>> False or True
True
>>> False or False
False

Only False or False gives False. Notice that or is also true when both sides are true: it doesn't mean "one or the other, but not both".

Outside a range

With or, you can check that a number is outside a range, below the lower limit or above the upper one:

number = int(input("Pick a number from 1 to 10: "))
if number < 1 or number > 10:
    print("That's not between 1 and 10!")
else:
    print(f"You picked {number}.")

12

Pick a number from 1 to 10: 12
That's not between 1 and 10!

A number can't be below 1 and above 10 at the same time, so number < 1 and number > 10 would never be true. When you check for a value outside a range, the operator is or.

A mistake that hides

Each side of or must be a whole condition, just as with and. This time, though, leaving out part of it doesn't cause an error, which makes the mistake hard to spot:

day = "Monday"
if day == "Saturday" or "Sunday":
    print("Weekend!")

Weekend!

Python reads the condition as (day == "Saturday") or ("Sunday"). The right side isn't a comparison at all, just a string, and in a condition Python treats any string that isn't empty as true. So the whole condition is always true, whatever the day. The fix is to compare the variable again: day == "Saturday" or day == "Sunday".