Genomic relationship matrix explanation

I am seeking the definition of the genetic distance matrices used in genomic prediction.

• What is the difference between a Rodger distance and kinship matrix?
• what people mean when they talk about genomic relationship matrix as in this paper:
  https://www.g3journal.org/content/9/5/1545#ref-30 , viz.

then we obtained the Cholesky decomposition of the genomic
relationship matrix