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
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b2b519-2ba77.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b2b519-2ba77.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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