Step 1: Compare it with a strike.
A strike is workers refusing to work, while a lockout is the reverse: the employer refusing to let workers work, both used as tools of pressure in a labour dispute.
Step 2: Note the effect on workers.
During a lockout, employees are kept out of the premises and usually lose their wages until the dispute between management and labour is settled.
Final Answer:
A lockout means management shutting the workplace to force a settlement of a labour dispute.