  Rowmotion is a simple cyclic action on the distributive lattice of order
ideals of a poset: it sends the order ideal x to the order ideal generated by
the minimal elements not in x. It can also be computed in "slow motion" as a
sequence of local moves. We use the setting of trim lattices to generalize both
definitions of rowmotion, proving many structural results along the way. We
introduce a flag simplicial complex (similar to the canonical join complex of a
semidistributive lattice), and relate our results to recent work of Barnard by
proving that extremal semidistributive lattices are trim. As a corollary, we
prove that if A is a representation finite algebra and mod A has no cycles,
then the torsion classes of A ordered by inclusion form a trim lattice.
