A foldable seat for a rollator or a wheelchair includes a first plate and a second plate. The plates are rotatably moveable between an unfolded position and a folded position.A hinge pivotally connects said first plate to said second plate. An exemplary hinge includes at least a first cylinder integral with said first plate and at least a second cylinder integral with said second plate.The seat further includes a locking/unlocking system configured to be actuated by the user so as to lock, respectively unlock, said first and second plates into, respectively from, said unfolded position and/or said folded position. The locking/unlocking system being at least partially lodged inside said first and/or said second cylinder.
