Softball questions are questions the interviewer asks to try to find out about your personality, your history, your level of enthusiasm, and your experience. While technical questions evaluate your skills or your knowledge, softball questions are meant to have you talk about less quantifiable abilities. An interviewer might ask a dozen or more softball questions to determine what you're like outside of an interview room.
The word to remember for interviews, especially the softball questions, is: STORIES. People who are good storytellers tend to be good interviewees.
Technical questions are important - you need the skills to be able to do the job. However, often interviewers are convinced by your answers to softball questions - then they spend the rest of the interview trying to convince themselves why they should hire you, instead of spending the rest of the interview trying to convince themselves why they shouldn't.
A great strategy for preparing for an interview is to review some softball questions and come up with 3-4 compelling and interesting stories that stand out from your education or from your career. Usually this handful of stories can be adapted to several questions. It’s usually OK to answer one question with a story and then later say, “Well, to answer that question, I’m going to go back to my story about…”
You don't need to memorize these stories, but being able to tell them in a manner that engages the interviewer will take you a long way toward getting the job.