The movement of particles in liquids and gases is referred to as

In a liquid or a gas the molecules are not held in fixed positions, so they move continuously in random directions and collide with one another and with anything suspended in the fluid. A small visible particle, such as a smoke particle in air or a pollen grain in water, is struck unequally from different sides at each instant, and so it jiggles along an irregular zig-zag path. This ceaseless random movement of particles in fluids is called Brownian motion, named after the botanist who first observed it, and it is the standard experimental evidence for the kinetic theory of matter.

The other terms describe something different. Translational motion is one particular type of molecular movement, namely motion of the whole molecule from place to place, and it is only part of the picture; it is not the name given to the observed random movement in fluids, and it says nothing about randomness. Vibrational motion is the to-and-fro oscillation of particles about fixed mean positions, which is characteristic of a solid, where the particles are too tightly packed to wander. An isobaric process is not a kind of motion at all: it is a thermodynamic change that takes place at constant pressure.

A helpful way to keep this straight is to link each state of matter to its dominant motion: solids vibrate about fixed points, while liquids and gases show free random movement, which is Brownian motion. Also note that Brownian motion becomes more vigorous when the temperature is raised or the suspended particle is smaller, because the average kinetic energy of the molecules increases and a lighter particle responds more to each uneven collision.