an area in a field of corn where the corn has been made flat in a regular pattern, often a circle or series of circles, which people sometimes believe has been done by aliens (= creatures from a different planet)

When corn circles first started to appear in Britain, no one knew how they got there. 麦田怪圈首先出现在英国，没有人知道是如何形成的。

Lundberg had been fascinated by the corn circles and believed they were made by alien landing craft. 伦德伯格对麦田怪圈非常着迷，认为是外星人登陆艇造成的。