postpone the trip旅行 means “trip” or “travel,” and 延期 means “postponement.” は marks 旅行 as the topic; the full expression is commonly used with する or にする to mean deciding to postpone the trip.
JA: 雨が続きそうなので、旅行は延期にしました。
EN: It looks like the rain will continue, so we postponed the trip.