A scoop is a small amount or portion, and in this context, it refers to a serving of vanilla ice cream that can be measured using a standardized volume such as a teaspoon or tablespoon.
Serve warm or at room temperature topped with scoop of vanilla ice cream. (epicurious.com)
Then I put a big scoop of vanilla ice cream on my serving with a little more caramel. (breadboozebacon.com)
It should also be noted that these cookies make for great ice cream sandwiches with a nice big scoop of vanilla ice cream placed between two of the colossal cookies. (spachethespatula.com)