concentration >> /ˌkɑnsənˈtreɪʃ(ə)n/
Definition: [noun] The action or power of focusing one's attention or mental effort.
Example: frowning in concentration
Definition: [noun] A close gathering of people or things.
Example: the largest concentration of Canada geese on earth
Definition: [noun] The relative amount of a given substance contained within a solution or in a particular volume of space; the amount of solute per unit volume of solution.
Example: the gas can collect in dangerous concentrations