What is Employee Engagement?

Legal Definition
Employee engagement is a property of the relationship between an organization and its employees. An "engaged employee" is defined as one who is fully absorbed by and enthusiastic about their work and so takes positive action to further the organization's reputation and interests.

An organization with "high" employee engagement might therefore be expected to outperform those with "low" employee engagement, all else being equal.

Employee engagement first appeared as a concept in management theory in the 1990s, becoming widespread in management practice in the 2000s, but it remains contested. It stands in an unspecified relationship to earlier constructs such as morale and job satisfaction. Despite academic critiques, employee-engagement practices are well established in the management of human resources and of internal communications.
-- Wikipedia
Legal Definition
Mental, emotional, and motivational connection an employee has towards the employing organization. It can be positive or negative. This is a gauge of an employee willingness to strive for organizational goals. It tends to influence the employees' behaviors and level of effort in work related activities. The more positive the connection an employee has with the organization, the more effort put forth. This also involves the nature of the job itself. Does the employee feels mentally stimulated? What is the level of trust and communication between employees and management? What is the ability of an employee to see how their own work contributes to the overall company performance? What opportunity of growth exist within the organization? What measure of pride does the employee have in the organization? How glad is the employee about working or being associated with this organization?