Printing Temperature Initial Layer refers to the temperature of the nozzle while it prints the initial layer.
You can set a slightly higher printing temperature for the initial layer than for the rest of the print.
This is useful to improve bed adhesion. The material will be more liquid at higher temperature. This allows it to flow out further, reducing the air bubbles below the print and increasing the contact area with the build plate.
This also allows the material to anneal a bit longer, which reduces warping.