what do the x-pixel size and y-pixel size mean in the file landstat.wdf

[Peter H.M. Jacobs]

Hello,

I'm convinced that this is realy a stupid question, but can anyone explain
to me what the x-pixel size and y pixel size mean in the file landstat.wdf

It says

30 #x pixel size
0000.000 #rotation x-as
0000.000 #rotation y-as
-30 #y pixel size
44364345.3453 # left upper corner
23424.23234   # right upper corner

Regads

Peter