Term
Centerline
Also called: Center Line
The line that splits the service courts into left and right.
The line that runs from the baseline to the non-volley zone line (kitchen line) and splits the service courts into left and right (3.A.4.d). There is no centerline inside the kitchen (3.A.4.d).
See it in a figure
This figure is from the rule "Court size and lines".
How to read the sources: numbers like (8.F.4) are rulebook sections, and links are outside sources. An "Author's note" is the author's personal experience, not an official rule.