1. A management action resisting employee's demands; employees are barred from entering the workplace until they agree to terms.
2. Industrial action taken by employers whereby they prevent workers coming to work. For example, they may lock out existing workers who have taken strike action but carry on producing by employing other workers.
3. A lockout is someone who looks out for someone or something that is dangerous or important
4. When a business locks out workers in order to prohibit them from working, it is a lockout.

The act of denying access to a given resource (file, memory location, I/O port), usually to ensure that only one program at a time uses that resource.