These are general terms used to describe defence. Some terms are specific to certain formations or tactics. But I'll explain that in more detail with the blog posts. And i'll show what formations and technique are used by the Ravens.
What is a defensive technique?
On defence where the linemen are positioned is called their technique.
It is determined firstly by where the offensive centre is. Lining up opposite the centre is 0. Lining up over either the right guard or the left guard is 2. Lining up opposite either tackle is 5. And opposite a tight end is 7. As you can see from the diagram below the shoulder of each guard and tackle also has a numbered technique. However to start the most common are:
0 - the nose or nose tackle.
3 - the 3 tech or defensive tackle.
5 - the 5 tech or defensive end.
7 or 9 - the defensive end or outside linebacker.
Some schemes or teams will use slight variations of the above. However I use the above as I think it's the most frequently used or basis for alternatives.
4-3 or 3-4?
Much like a 4-4-2 or 4-5-1 formation in soccer this represents the formation the defence plays. It refers to the number of players who line up at each position, starting with those closest to the ball.
3-4 = 3 defensive linemen and 4 linebackers (plus four defensive backs so could be considered a 3-4-4)
4-3 = 4 defensive linemen and 3 linebackers (plus four defensive backs so could be considered a 4-3-4)
I include the defensive backs because for more complicated formations the term is used with them included.
Mind the gap.
The defence use letters to refer to what their role is on each running play. The running back is trying to run between the gaps his offensive linemen are creating. Therefore to counter this the defence want to fill each gap and leave no space to run into. Using the same diagram as before this time looking at the black letters to name the gaps:
The gap either side of the centre is the A gap. Between the guard and centre is the B gap and between the tackle and tight end is the C gap.
There is often a player who is responsible for the running play not getting to the flanks outside of the C gap. Stopping the run outside to the flank is called setting the edge or keeping contain.