.*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): numbers, letters, other special characters, etc.
Read more about pattern matching in COPY INTO command.