A scheme in football is a strategy a team uses on offense and defense to be successful in football games. Schemes are usually collections of different offensive and defensive plays for each team to use. Think of it like a team's playbook where they can choose any offensive or defensive formation depending on the game situation and their opponents. Schemes are usually created or further developed by the offensive and defensive coaching staff.
The most common schemes that players and fans typically recognize are the 4-3 and 3-4 defense, and the zone or man-to-man defense. These are four types of defensive formations that a coach can call. Each scheme is usually interchangeable with the name of the offensive or defensive formation, but other times the schemes can become more specific if the quarterback calls a scheme that involves a particular player or block. Sometimes schemes are called when quarterbacks hope for specific outcomes with individual players, where other schemes are more generalized and involved the entire offense or defense.
Many coaches will choose a scheme depending on the lineup on the field. If certain players excel in a particular area, it would be beneficial for the team if the coach called a scheme where players can shine and outperform their opponents.