Rshares are reward shares, that is the share of the reward pool allocated to a post by voting.
If you look at a post on steemd.com and click on properties and vote details you will see a table with all the vote information.
One column is rshares. The larger the number, the greater the amount of reward shares, the more of the voting pool that is allocated to your post.
I assume SBI have an amount of voting power and allocate their rshares (i.e. their voting power) between all the SBI users.