Confused about definition of bulk flow of water by osmosis
Bulk flow and osmosis are different; I'm guessing your text might be talking about using osmosis to drive bulk flow, but they are occurring at different stages.

For example, if you get your water from a water tower, your house's water pressure is driven by gravity. However, the water tower could be filled by an electric pump. You could say your water pressure is driven by an electric pump, but the pump isn't really pushing water into your house, it's just pushing water up a tall tower so that gravity can act, and if you didn't realize this fact you might be confused about how you can still have water pressure even when the power goes out.

Similarly, you can drive bulk flow by osmosis. If you have a closed space (e.g., a "tube") and pump salt (or anything else water soluble) into it, it can pull water from the surrounding tissues via osmosis. As the pressure of water increases in that closed space, it can now flow in bulk through that tube. Plants can use this mechanism to deliver nutrients up a stem: they pump in ions/molecules inside the stem, which pulls in water from the soil around. Because the space is rigid, instead of expanding the water goes up the stem in "bulk": anything else carried in the water will be pushed up with it. Then, when target tissues pull in solutes, osmosis again causes water to follow, and by only pumping solutes in one place and out another you produce a bulk flow of water.