Learner's definition of CONCENTRATION
1 [noncount] : the ability to give your attention or thought to a single object or activity : the ability to concentrate
the power of concentration
All that noise is disturbing my concentration.
The job required her full concentration.
When you're tired it's easy to lose your concentration.
2 : the act of giving your attention to a single object or activity
3 a : a large amount of something in one place
[noncount] b [count] : a large number of people in one place
4 [count] : the amount of an ingredient in a mixture
Contaminants were found in low concentrations. [=amounts]
measuring the concentration of salt in a solution
They detected high concentrations of pollutants in the water.