Answer: Gain.
Explanation:
Suppose that you buy a given stock at $1 the share.
Now, if the stock increases (because of a given change, one example can e that the demand of a given object increases, and it impacts on a increase in the value of a given stock)
now, each share of the stock has a sligthlt bigger value, suppose it is $1.05
now, this means that the shares that you already have increased the value, so you have a gain of $0.05 per share.