A stack is LIFO (last in, first out). Think of it as a stack of books. As you pile them up, you always take the first one off the top or you topple the stack. A queue is FIFO (first in, first out). Think of it like a line for a ride at an amusement park.

This example uses a stack in an efficient way for Python. That is, the top of the stack is the end of the list. Calling pop removes an entry from the end of the list. Calling append adds an entry to the end of the list.

https://en.wikipedia.org/wiki/Stack_(abstract_data_type)
https://en.wikipedia.org/wiki/Queue_(abstract_data_type)

Using a good font is good, @ksqsf, true. However, single character variable names are problematic in most places for other reasons, and so it's good practice to mostly avoid them. In longer code blocks, you start to wonder was "l" length? List? Lemurs?

"Good enough is perfect" is often a recipe for tech debt. While I will agree that perfect is the enemy of good, your argument that this is a best practice is flawed. This is a solution that works. It is not a best practice.