The Vietnamese word "hải yến" refers to a "salangane," which is a type of bird known for building nests that are highly valued in Vietnamese cuisine, particularly for their nests that are used to make bird's nest soup.
While "hải yến" primarily refers to the salangane bird, in some contexts, it might be used metaphorically to symbolize delicacy or something that is highly valued, similar to how the nests are perceived.