.*string.* - matches all files which contain the given string. Eg : abc_string, abc1_string23, string_abc.
.* – matches one or more occurrences of any character, including no character.
? – represents or matches a single occurrence of any character.
[ ] – matches any occurrence of character enclosed in the square brackets. It is possible to use different types of characters (alphanumeric characters): numbers, letters, other special characters, etc.
Read more about pattern matching in COPY INTO command