What is the definition of micro-poem?

In fact, it seems that there is no clear regulation, that is, the word "micro". Therefore, this competition is also based on the relevant situation, because it is based on Xu Zhimo's fame, so draw a line for four catchy sentences in Xu An's poem Farewell to Cambridge. Of course, three or two sentences or even one sentence will do, but it can't exceed four lines. Otherwise, there is no specific standard.