Topband: What is the meaning of the term "geomagnetic absorption"?

[Sam Dellit]

g'day to all on the topband reflector

excuse my apparent ignorance but i am not familiar with the term
"geomagnetic absorption"

is there a difference between this term and the more commonly encountered
term "ionospheric absorption"

or is it now being used as a shorthand term for "excess polarization
coupling loss"

an explanation would be appreciated

73s gd dx de sam dellit  vk4zss