The title is a pun based on the fact that Norman Buntz is running the precinct in the absence of Frank Furillo and Henry Goldblume. Historically, the term refers to the Norman conquest of England in 1066 AD by William, Duke of Normandy, and his victory at the Battle of Hastings. The Norman invasion of England was significant because this was the last successful military invasion of England to the present day. Sadly, however, this episode during the series's last season (the 7th season) showed the slow decline of the series once it passed its prime. The story lines are fairly absurd and all less than compelling.
Sid tells Buntz "you're flying high in April, you're shot down in May". These are the lyrics to the song "That's Life" sung by Frank Sinatra.