1. the ability to focus one's attention or mental effort on a particular task or subject
2. the action of focusing all one's attention or mental effort
3. a large amount or number of something in a particular area or place

Examples

• The student's concentration improved after removing distractions from her study area.
• Deep concentration is required to solve complex mathematical problems.
• There was a high concentration of restaurants in the downtown district.
• The concentration of salt in seawater is about 3.5 percent.
• His concentration was broken by the loud noise outside.
• The concentration of wealth in certain areas has increased over time.
• Scientists measured the concentration of pollutants in the water sample.