广纳百科
A loop is a circle, or a round path. If you tie the two ends together of a string, you get a "loop". A key point of a loop is that it has no beginning and end. In another word, loop is a path that its end is its beginning and its beginning is its end.
Loop是使循环，使成环，重复执行的意思。是抽象意义层面的圈。之所以说是抽象意义的圈，是因为loop强调的是无始无终，换句话说就是开始即是终点，终点也是开始。
接触过计算机编程的人都听说过while loop， for loop这样的表达，之所以此处使用loop来代表循环，是因为while循环、for循环在满足跳出语句(break)的条件时，当前的循环将停止执行。 如果不满足跳出条件，代码将一遍一遍的重复执行下去，也就真的变成了循环了。 程序在执行循环的过程中，是无法预料是执行多少遍代码才能跳出循环结构的。也许一遍，也许两遍，也许三遍，也许永远循环下去。 无始无终的概念就是这样诠释的。
Examples:
She setup her cellphone to loop the music because she love it.
Write a while loop (computer programming term)
Imagine you are drawing a circle with your finger, you will complete a cycle when your finger move back at the point where you started your drawing. Cycle is kind of an activity to show something goes back its beginning.
设想你用手指画圆圈，当你的手指回到了一开始起笔的那个点时，说明你完成了一个cycle。因此cycle强调的是有始有终，强调的是一个事物经过了不同的时期又回到了原来的初始状态。
比如自然界液态水经过不同状态的变化又重新变成了液态水的整个过程就是一个cycle。
Water cycle: water (snow, rain...) - vapor - cloud - water (snow, rain...)
Product Cycle 产品周期
Season Cycle 季节周期
