The page 2 of Percolation by Bollobas et all (2009) contains this picture
where the left is for the site percolation and the right for the bond percolation. The filled circles on the left are open sites. The author is trying to demonstrate open subgraph. I cannot understand the difference between the two pictures: why black/white circles on the left while only black cricles on the right? So
Are sites in bond percolation always closed?
Bond percolation and site percolation are visualised as this in Mathworld
where the bonds are the edges and the sites are the squares.