The term "alien spacecraft" refers to a vehicle that is not of this world. It is often used in science fiction and conspiracy theories. However, there are several synonyms for this term that can be used interchangeably, depending on the context. Some of these synonyms include "extraterrestrial craft," "UFOs" (Unidentified Flying Objects), "flying saucers," "interstellar ships," "space vehicles," and "spacecraft of unknown origin." Each of these terms differs in connotation and can strengthen or weaken the sense of mystery and unease that surrounds the concept of alien life. Nonetheless, they all suggest the existence of advanced technology beyond our current level of understanding.