A soccer pitch can be drawn into thirds in order to easily describe where the action is taking place. Coaches use thirds to plan drills, plays, and strategy. Let's try and understand the layout of the field by breaking it up into three distinct parts.
The defensive third of the field refers to the side containing a team's own goal and penalty area. One team's defensive third is the other team's attacking third. You can think of it like this, if your team is playing defense on the side of the field where their own goal is, then they are in their team's defensive third.
The middle third refers to middle of the pitch surrounding the halfway line. In the middle third, you will likely find midfielders moving between the defensive third and attacking third. When a team is on offense, they are trying to bring the ball into the attacking third and prevent the other team from stealing the ball and moving into their defensive third. There is a lot of movement in the middle third and it is a place of heated contest.
The attacking third refers to the area containing the opposing team's goal and penalty area. One team's attacking third is the other team's defensive third. You may sometimes hear the attacking third called the final third because it's the final destination or place the offense needs to go in order to score a goal.