Bernoulli's principle states that an increase in the speed of a fluid decreases its pressure. Therefore, the speed of a moving fluid is the primary characteristic that determines its pressure.

Here's a breakdown:

* Faster Fluid, Lower Pressure: When a fluid flows faster, the particles within it have less time to exert pressure on the surrounding surfaces. This results in lower pressure.

* Slower Fluid, Higher Pressure: Conversely, when a fluid flows slower, the particles have more time to exert pressure on the surrounding surfaces, leading to higher pressure.

It's important to note that Bernoulli's principle is based on the conservation of energy. The principle considers the trade-off between the kinetic energy (energy of motion) and potential energy (pressure energy) of the fluid.