CNN Notation "conv4_3" When a CNN layer is referred as convX_Y (e.g conv4_3), what do X and Y stand for? Is it simply just the layer name, and nothing to do with the details of the layer? For example: in the SSD paper by Liu et al.

The notation convX_Y refers to the identification of the convolutional layer.
See the VGG-16 network as an example. The convolutonal layers that occur in sequence prior to a pooling layer have the same X identifier and different Y identifiers. After the pooling layer, the X identifier is incremented, and this naming convention is repeated.
https://icmlviz.github.io/icmlviz2016/assets/papers/4.pdf
