What refers to the stock of employee skills, knowledge and capabilities that may not show up in a balance sheet but have significant impact on a firm's performance ?

The correct answer is human capital. 

Key Points

• Human capital is an intangible asset not listed on a company's balance sheet.
• Human capital is said to include qualities like an employee's experience and skills.
• Since all labor is not considered equal, employers can improve human capital by investing in the training, education, and benefits of their employees.
• The term human capital refers to the economic value of a worker's experience and skills.
• Human capital includes assets like education, training, intelligence, skills, health, and other things employers value such as loyalty and punctuality.
• Human capital is perceived to increase productivity and thus profitability.
• The more investment a company makes in its employees, the chances of its productivity and success become higher.

Additional Information

•  Human resource planning (HRP) is the continuous process of systematic planning ahead to achieve optimum use of an organization's most valuable asset—quality employees. Human resources planning ensures the best fit between employees and jobs while avoiding manpower shortages or surpluses.
• Human resource management (HRM) is the practice of recruiting, hiring, deploying, and managing an organization's employees. A company or organization's HR department is usually responsible for creating, putting into effect, and overseeing policies governing workers and the relationship of the organization with its employees.
• The number of employees refers to the total number of full-time employees an enterprise employs during a calendar month.

Hence, Human capital refers to the stock of employee skills, knowledge, and capabilities that may not show up on a balance sheet but have a significant impact on a firm's performance.