What does grid segment x mean in kml file?

Question

Database design

A file with weather data has arrived. Value and Coordinates, line type, polygon are described in the file itself.
The file has something like this: 10102018_pp_y_rusp_980.kml
Where the date of the weather comes first, then the weather is pp-pressure, and y is the grid segment y..etc.
Note: in addition to y, one of the values ​​\u200b\u200b(y, z, x, u, s, w, t) can also be indicated there.
I read the instructions from Google, but did not understand all the same. Please tell me, preferably with an example, what kind of information is this, a node segment ... (x, y, z, u, s, t, w)?