It is a date that is written or read in the same way from backwards or forwards. For example, 01.02.2010.
And there is another day called “Global Palindrome Day” where the date is the same in both US (MM/DD/YYYY) and UK (DD/MM/YYYY) formats. For example, 02.02.2020. In this case, it is also the same in the Chinese format where they follow YYYY/MM/DD format.