What is a capacity?

Answer 1

• capability to perform or produce; "among his gifts is his capacity for true altruism"; "limited runway capacity"; "a great capacity for growth"
• capability: the susceptibility of something to a particular treatment; "the capability of a metal to be fused"
• the amount that can be contained; "the gas tank has a capacity of 12 gallons"
• the maximum production possible; "the plant is working at 80 per cent capacity"
• a specified function; "he was employed in the capacity of director"; "he should be retained in his present capacity at a higher salary"
• (computer science) the amount of information (in bytes) that can be stored on a disk drive; "the capacity of a hard disk drive is usually expressed in megabytes"
• capacitance: an electrical phenomenon whereby an electric charge is stored
• the power to learn or retain knowledge; in law, the ability to understand the facts and significance of your behavior
• tolerance for alcohol; "he had drunk beyond his capacity"

I think it is the amount of the substance. A bit like mass. I hope this helped.