LittD is an abbreviation for "Litterarum Doctor" or, in English, Doctor of Letters (or Literature). Most American universities only give the LittD as an honorary degree; it's bestowed upon people who have made some great contribution to literature. (Harvard, for example, has given honorary Doctor of Letters degrees to Robert Frost, Carl Sandburg, and Tennessee Williams.) Some universities in Australia, Europe, and New Zealand have programs that allow people to earn the degree (which they rank above the PhD); as with the DSc, applicants must demonstrate that they've produced some great work of literature or made a long-lasting contribution to their field. It's a degree awarded to someone not at the start of their career, but in the middle or near the end.