Coach Nana explains how defensive gaps are identified and named, which is crucial for a linebacker's responsibilities. Gaps are the "holes in between the O lineman" and are called by letters, such as 'A gap,' 'B gap,' or 'C gap'. The naming starts from the center and mirrors out on both sides of the offensive line. The 'A gaps' are directly next to the center, the 'B gaps' are between the guard and the tackle, and the 'C gaps' are outside of the tackle. If the offense uses a tight end, the gap outside the tight end is called the 'D gap'. When a tight end is on the field, the defense will call the strength to that side, using terms like 'strong right,' and refer to the specific gaps as 'strong A gap,' 'strong B gap,' 'weak A gap,' and 'weak B gap'.