What is meant by the concentration of an industry? How is concentration measured? What are likely causes of high concentration?

What will be an ideal response?

Industry concentration means that a relatively large share of the industry's output is produced by the largest firms in the industry. It is often measured with concentration ratios. The four-firm concentration ratio is the percentage of total industry sales generated by the four largest firms in the industry. High concentration is likely to be associated with economies of scale, barriers to entry, and a history of mergers.