Lower means closer to the field. So lower box seats are box seats that are closer to the field than upper box seats. Box seats are usually reserved seats that consist of separate "chairs" for each ticket-holder. Box seat are sometimes called "loge seats," but this is rare for a sports stadium. The term loge is more common in opera houses. Box seats can be compared to unreserved seats, which usually consist of just a number on a long bench. In baseball, the unreserved seats are commonly called the bleachers and are behind the outfield fence. So, lower box seats are reserved, close to the field, relatively comfortable, and more expensive than upper box seats or unreserved seats. If you want to see a layout of Fenway Park, you can search for "Fenway Park layout." For instance, here is one: http://www.preciseseating.com/fenwaypark2.php