Unless you specify otherwise sort treats the one or more space characters between words as field delimiters. You may want to sort files where words are separated by another character such as a colon (:).
Use the -t option to specify another character to act as the field delimiter. For example
specifies the colon (:) character as the delimiter.
One specific delimiter followed by another indicates an empty field. For example with a colon (: ) as a delimiter
field2 is taken to be empty.