Capiral L vs small l

I somehow thought I understood the difference but now I don’t anymore!
When is capital L used and when is small l used??

I tought capital L is for the loss functions and small l for the number of layers. however, in this video that is not how they are used.

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They are not used consistently.
For a neural network, ‘L’ usually means the number of layers. But in general ‘L’ can refer to the loss.
J is more often used for the cost.
‘l’ is not used very often.