FIMI was created because there was a problem the EEAS was faced with: there were many different terms for similar phenomena (fake news, disinformation, computational propaganda, coordinated inauthentic behavior). While each were useful they did not cover the exact problem the EEAS was mandated with dealing with. The EEAS had a mandate to counter influence from authoritarian countries who were using the internet to influence public discourse.
The formal definition, according to the EEAS who first developed the term, is:
"Foreign Information Manipulation and Interference (FIMI) describes a mostly non-illegal pattern of behaviour that threatens or has the potential to negatively impact values, procedures and political processes. Such activity is manipulative in character, conducted in an intentional and coordinated manner, by state or non-state actors, including their proxies inside and outside of their own territory."
The goal with the definition of FIMI was to focus on manipulative behaviors rather than narratives. Additionally, this allowed them to draw from developments in Cyber-Security that were linked to disinformation (eg. MITRE as a way to describe behaviors). This linked it with taxonomy tools such as the DISARM Framework, which could be used to describe disinformation behaviors.
So let's break it down, what do they mean by "mostly non-illegal"? Much of the patterns of behavior used in manipulation campaigns are not illegal. For example, setting up fake accounts or creating a deepfake is not illegal. Some actions are illegal like hacking into secure networks to search for information. The term was also a starting point to encourage the enactment of legislation around what could be legal or manipulated.
A "pattern of behavior" refers to the specific techniques used by the campaign.
Next the “Threatens or potentially impacts values, procedures, and political processes" is meant to indicate that FIMI is primarily aimed at political disinformation. However, they also outline that they address health disinformation, environmental disinformation and disinformation that poses a threat to security.
Finally "Manipulative, intentional, and coordinated" covers the use of deception, the perceived intent of the campaign and whether it operates with planning and coordination rather than being organic.
In total FIMI encompasses threat actors that: (1) use deception, (2) intent to harm, (3) can be identified as groups or entities, and (4) follow patterns.
This is the brief definition of FIMI. As you'll notice it contains many parts some of which can be left open to interpretation (such as how are "values" determined?). The definition suited the EEAS's mandate for what they were tasked with accomplishing
