In vue, can you explain the error caused by using the _ c variable?

Today, when I was writing a demo, I was doing a for loop, and then I used _ c as a variable name, and then VUE reported an error. I tried to change _ c into c, _ a, _ d and so on. If I use _ c, I will report an error. Excuse me, what is the reason for this?
BUG? of VUE itself

_ c reported an error.

Mar.02,2021
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