From the game's encyclopedia
Innovations are technologies and other advances that benefit all characters of a certain Culture. Innovations are grouped into the Eras when they can be discovered.
Through contact with neighboring Cultures, each Culture is always Spread to one specific Innovation which will be discovered much quicker.
In addition, the Culture Head can set another (or the same) Innovation as the Cultural Fascination for an additional boost.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Innovation is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Innovations are technologies and other advances that benefit all characters of a certain Culture." The game also links it as Innovations. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.