Does the "lowest layer" refer to the first or last layer of the neural network? People sometimes use 1st layer, 2nd layer to refer to a specific layer in a neural net. Is the layer immediately follows the input layer called 1st layer?

How about the lowest layer and highest layer?
Lowest layer generally refers to the layer closest to the input. This comes from the idea that layers closer to the input represent low-level features such as gradients and edges, while layers closer to the output represent high-level features such as parts and objects.