intersitial是什么意思

1 : situated within but not restricted to or characteristic of a particular organ or tissue —used especially of fibrous tissue
2 : affecting the interstitial tissues of an organ or part <interstitial hepatitis>
3 : occurring in the part of a fallopian tube in the wall of the uterus <interstitial implantation> <interstitial pregnancy

好象没这个单词，是专有名词吗？？