1the other day; recently — referring to a recent time or a short while ago.
この間、田中さんに会ったよ。
I ran into Tanaka the other day.
この間買った本が面白かった。
The book I bought recently was interesting.
この間は忙しくて返信できませんでした。
I was busy recently and couldn't reply.
2meanwhile; in the meantime — a somewhat formal/literary word referring to the period during which something else is happening.
彼が入院していたこの間、会社の状況はすっかり変わってしまった。
While he was in the hospital, the situation at the company changed completely.
留学していたこの間に、日本語がずいぶん上達した。
During my time studying abroad, my Japanese improved a great deal.
戦争が続いたこの間、多くの人々が苦しんだ。
During the period the war continued, many people suffered.