星际 (xīng jì) is an adjective meaning 'interstellar'—referring to the vast space between stars. It combines 星 (xīng), meaning 'star', and 际 (jì), meaning 'boundary', 'edge', or 'region between'. Together, they literally suggest 'the region between stars', capturing the immense, empty expanse of outer space beyond planetary systems.

This term is commonly used in scientific, astronomical, and science-fiction contexts—especially when discussing phenomena like interstellar travel, interstellar dust, or interstellar communication. While it can occasionally appear as a noun (e.g., in compound nouns like 星际旅行), its primary grammatical function is adjectival, modifying nouns such as 航行 (voyage), 物质 (matter), or 空间 (space). It carries a formal, technical tone and rarely appears in casual daily conversation.