These two terms are often misused and misunderstood on a regular basis.

Another commonly heard criticism is that "the back four were too flat". This is also confused by the term "play a flat back four". In fact, a back four should never be flat, except for the brief purpose of playing offside. Someone should always be covering (drop off a couple of yards): this varies depending on where the ball is. If a forward spots this and moves in behind another defender, the player simply steps up to catch him offside (see the diagram on the next page for an explanation). For this brief time the back four is flat but as soon as they can a defender will again drop off to offer cover. It is a "cat and mouse" game between the defense and forwards. The advantage is with the defense as they can determine the offside line and trap forwards who try to exploit the space provided by a player dropping off to offer cover. How far back to drop depends also on the speed and ability of the forwards of the opposition. It also presents problems for a team when mounting an attack.

These two points are emphasised by Ron Atkinson (Monday March 10, 2003 The Guardian).

Thierry Henry's substitution played a massive part in helping Chelsea to equalise. When the Frenchman went off with cramp in his calf it not only took something away from Arsenal but made it far easier for Claudio Ranieri's team to mount the pressure that earned them a replay. The key is that Chelsea's back line was able to squeeze up a lot more, making the team more compact and giving them less distance to cover to mount a real threat had to defend deep because of the danger he poses with his pace if he's given acres in Arsenal's goal when they went forward. While Henry was on the pitch, Chelsea of space to run into over the top. The problem of holding a high line against Henry was shown with his goal. Defending deep meant Chelsea were stretched as a team and had a long way to travel with the ball to trouble Arsenal when they won possession at the back.

Ron Atkinson also identifies the dangers of a high back line and the need for a solid defense (Monday February 24, 2003 The Guardian).

Manchester City gave the worst display of defending I have ever seen... their back line held a dangerously high line and I can't remember City making one decent challenge for the ball... but it's interesting to note that it was the team with the best defense, Valencia, who won the Spanish league last season. At the end of the day people know it's very difficult to win things with a ropey defense.

The next time someone uses these terms ask them what they mean. It is often the case that they are talking nonsense!