What are the various concepts of Working Capital ?

Answer 1

working capital refers to Current Assets-Current Liabilities

Answer 2

Current assets - Current liabilities = Working capital.
Usually you should have it small since working capital is usually financed by borrowing which has high interest cost and so is risky since it raises the financial leverage of a compay and hence the financial risk.
Japanese have found a way around it to keep it low by the JIT or just in time method where the iventories are kept low. By doing so current asset gets low and working capital gets low thus reducing financial risk of companies.
Usually in US working capital is financed using 'compensating balance' method a money market instrument. The interest cost on this is prohibitively high.
Sometimes working captial turn over is a performance ratio companies use when planning operations or control. The lesser the working capital the higher the ratio and more sound the performance.
Working capitals are sometimes planned in advance by efficient companies so that their growth is carefully monitored to reduce the risk in operations of the company. Good inventory control, efficient cash management, Accounts receivable control etc; and managing accounts payable by creating delays in payment etc; or what one calls increase in cash cycle ie; reducing accounts receivable delay and increasing accounts payable period maximal efficiency of cash employed is achieved.
The rest involves lot of other theories.