Description: 我们周围的空气每立方厘米含有大约 1000亿亿个分子。理想的真空应该是不含任何分子的区域。但实际上，如果一个区域内粒子比通常情况下少得多，我们就可以称之为真空。“高真空 ”每立方厘米的粒子数只有通常的百万分之一，而 “超高真空”每立方厘米的粒子数不到 10 亿。外太空的大部分区域甚至比这还要空。平均而言，宇宙中普通物质粒子的密度不到每立方米一个。那些被天文学家认为密度相对较高的物质，如巨大的分子气体云，仍然比我们在地球上所能产生的任何真空更“空”。

Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher
The translation of this term and its definition is still awaiting approval

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".