This is the 993rd most frequent Japanese word.
緊急
"緊急" means "urgent" or "emergency."
Here, '緊急' modifies '事態' (situation) to indicate an emergency situation.
緊急事態には冷静に行動する必要があります。
During an emergency, it's necessary to act calmly.
'緊急' is contrasted with 'ではない' (not), referring to matters that are not of an emergency nature.
緊急ではない案件は後で処理してください。
Please handle non-urgent matters later.
In this sentence, '緊急' works as an adjective describing '連絡' (contact), meaning it was an urgent communication.