"performance gaps" can be defined as :

a. features of a product that are better than expected
b. features of a product that do not perform as promised
c. the reasons why product has performed well
d. positive engaging material for the audience of the review

The performance gaps could be defined as lost battles in a war. They can occur due to the product's features and/or other circumstances. Thus the answer of the question is:

b. features of a product that doesn't perform albeit used according to the terms of use

it is the background information on the characters and setting explained at the beginning of the story. the exposition will often have information about events that happened before the story began. the exposition is often the very first part of the plot.