Answer: The terrain, or land, in a particular area.
Topography refers to the study of the features of land. It is often considered synonymous with relief when the term is used in maps with elevation contours. The excerpt explains that topography can alter the average range of weather radios. It then goes on to cite mountainous terrains as one example of how topography can impact the radio. Therefore, the meaning of the word can be guessed from the text.