Trim can be used to remove unnecessary white space, white space means the space or tab character.
The Select metadata fields to modify option specifies the fields to apply trim.
If a fields start with whitespace this can be removed by enabling Trim whitespace from start.
If a field ends with whitespace this can be removed by enabling Trim whitespace from end.
If a field contains multiple whitespace characters in a row this can be reduced to just one space character by enabling Trim multiple whitespace characters to one