One of the very first things we learn in Ip Man style Wing Chun is the centerline (Chung Seen, 中线). In Yuen Kay San Wing Chun their centerline is called the meridian line (Jee Ng Seen, 子午线).

Why the difference in name?

Is it a case of tomahto tomayto?

In the chapter You Don’t Know Until You Know You Don’t Know I take a look at this question. I conclude that the trio of centerline, central line and meridian line are the same thing.

However, in one lineage there is a difference between centerline and meridian line. They also have a more sophisticated and delineated way of mapping out the lines of attack and defense.

One of the mapped lines remind me of how TWC folks explain their central line. The difference is that in TWC when explaining the central line instead of positioning their body squarely they would turn the body to do so.

However, in this one lineage they can explain the difference between centerline, meridian line and this line that reminds me of the central line while the body is facing square on. To them to tomahto is not tomayto.

This is a case of what I would call you don’t know until you know what it is that you do not know.

P.S. – if you wonder why you have never heard of this information the reason is because this lineage has gone out of their way to keep their knowledge away from the public. Their late grandmaster had noted that fellow students can end up not talking to each other when a style becomes famous and the politics come along with it.