The word 后卫 (hòuwèi) is a compound noun formed by combining two characters: 后 (hòu), meaning "behind" or "rear", and 卫 (wèi), meaning "to guard" or "defend". Together, they create a literal meaning of "rear guard", a term originally used in a military context for troops protecting the back of a formation. By semantic extension, this logical structure is applied to modern contexts, most commonly in sports like soccer and basketball, where it directly and intuitively denotes the "defender" or "full-back" players positioned at the back to guard their team's goal or basket.