Employment at will is a way by which an employer can layoff his employee any time on any grounds which should not be illegal. Termination grounds may or may not provide any reason for the employee. Similarly, an employee can also leave his/her job without any reason and this has no bad consequences.
The word employment will define this within its words that any employee at any firm/organization can leave without facing any bound by their employer and vice versa.
Though the term employment at will is a term which has been contracted and signed by both the parties; (employer or an employee) but still it is on the employer to terminate his/her employee. Similarly, it is on the employee that he/she might leave a job any time.
