What builds up along with charge?

When charge builds up, it creates an electric field which leads to a difference in electric potential energy between two points; this is what we refer to as voltage. Voltage is essentially the measure of electric potential energy per unit charge and indicates the ability to do work by moving charges through a circuit or a conductive path.

In practical terms, as charge accumulates in a region, such as in a capacitor, the voltage across the capacitor increases. This is a fundamental principle in electromagnetism, where charges exert electric fields and those fields result in the potential difference, or voltage, that can drive current in a circuit.

The other options do not directly relate to the buildup of electric charge. For instance, pressure is a measure of force per area and is more commonly associated with fluids. Heat is a form of energy related to the motion of particles in matter but is not a direct effect of charge accumulation. Mass pertains to the amount of matter in an object and does not change due to electric charge buildup. Thus, voltage is the appropriate concept directly associated with the accumulation of charge.