Fetching details from the dictionary...
turning point; change; transition; turn (of the tide, century, etc.)
人生の変わり目が訪れた。
A turning point in life has arrived.
季節の変わり目に風邪をひく。
Catch a cold during the seasonal change.
世紀の変わり目が近づいている。
The turn of the century is approaching.