Editorial independence refers to the separation between a media outlet's owners or advertisers and the decisions its journalists and editors make about what to cover and how to cover it honestly. It is meant to ensure that commercial or political interests do not quietly steer the news that ultimately reaches readers.
In well run newsrooms this separation is often formalised through internal policies, sometimes called a church and state divide between the editorial and business sides of an organisation, so that advertising relationships or ownership preferences cannot dictate story selection or framing in any meaningful way, which is worth remembering in most contexts.
Readers rarely see editorial independence directly, since it shows up as an absence rather than a feature: the absence of favourable coverage that was clearly bought, and the presence of critical reporting even when it is genuinely uncomfortable for the outlet's own commercial backers or owners to read about.