There is no single definition of employee engagement because it’s lots of things depending on what you’re selling, what you want, and what matters at the time. Often though, employee engagement is defined as some version of commitment to the organization and a willingness to give discretionary effort at work. See here, here, here, and here. Sometimes “discretionary effort” is called “going the extra mile,” like here.
The problem with defining engagement as employees giving something extra is that it’s too easy to expect them to work for free. Expecting discretionary effort for every employee subject to overtime becomes a wage hour issue.
