Deflection is flex.
All forks do it.
A fork with lots of deflection is flexible, and can feel squirrelly or soft for heavier riders, but may be perfectly matched for lighter riders or riders who want a little more comfort. A fork with very little deflection is stiff. A stiffer fork can be jarring over bumps, but often is more precise in handling. It's not, really. There are other factors that go into a decision of which aftermarket fork to buy, if any.