What is the meaning of the singular/plural syntax in, say, ng-repeat="product in store.products"?
Singular/plural is used just for common sense and code readability - it doesn't have to be singular/plural. You can do
ng-repeat="whatever in store.products"`
and then have the whatever object available inside (like: <img ng-src="{{whatever.images[0]}}" />).
In your case, store.products can't be changed since it refers to an actual object, while product is a completely custom name to be used in the repeat loop.
Fairly common in programming. Like the other answer said, it's similar to the for..in syntax.