Flow of holes in transistor?
Holes are spaces where an electron could be but presently is not. Like any hole in the macroscopic world, you can't move one; it's an absence. All you can do is fill the hole, which creates a new hole somewhere else. We can in some ways model this as an imaginary particle that's flowing the opposite direction from the electrons (and thus in the same direction as the current), but there's no actual particle moving in that direction. Like most models, it's a convenient fiction that makes the math easier.