Not everyone uses them, but many scholars and critics of the field find them useful in discussion and the analysis of sf texts. I will expect you to apply them to the stories we read and the movies we watch. In geometry this term means using a set of points to draw a curve that extends beyond the last known location. The points the science fiction writer starts from are observations of past and current conditions. The extrapolated curve is a hypothetical future trend that follows logically from them.
Writers extrapolate from both scientific knowledge and social patterns.
Basically, when a sf writer extrapolates he takes some idea or object or condition in his world and projects it into the future and speculates on how it might change. To feel estrangement is to feel separated from something. An estranged husband and wife are separated, for example. With science fiction the term is used to describe the feeling a reader has when he reads a sf story. Something is unfamiliar, unusual, or weird, and he is therefore estranged from the world in the story.