Plant Skills and Overgrowth Path of Exile 2 game term
Plants created by Plant Skills can be Overgrown to gain power in ways detailed on the Plant Skill. This generally cannot be caused by the Skill that creates the Plants, and requires a different Skill or effect that specifically causes them to Overgrow.
The game's own definition, as shown when you hover the term in game.
Game data: Path of Exile 2 client · How we source this
Plants created by Plant Skills can be Overgrown to gain power in ways detailed on the Plant Skill. This generally cannot be caused by the Skill that creates the Plants, and requires a different Skill or effect that specifically causes them to Overgrow.