It stands for search engine optimisation - it's an old-school method that was very popular pre-2016. The theory was that you could drive your website organically up the Google search rankings by publishing articles which mentioned certain key words that people were searching for and therefore drive trfafic to your website.
Google changed it's algo in 2016 and again in 2021 to combat this 'old school' SEO manipulation and it's not really a thing now although people still talk about it.
'New school' SEO is more about using different types of content (video etc) and packing the content with social media signals to drive the content up the rankings.
The Indie and ES websites are ~sort of~ doing this, but the fact is that if their Rose Hanbury articles are ranking high atm, it's likely that the public is just really really interested in Rose Hanbury just now due to the rumours.