Jack of all trades = One who is doing (or is capable in doing) many different jobs or business = άνθρωπος για όλες τις δουλειές.
       
Jargon = The informal terminology invented and used by a specific department or a specific group of people with the same specialty working at different companies targeting to the faster and easier communication among them

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Jet lag = The dizziness being created by the time difference of long distance flights

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Job satisfaction = The satisfaction one gets from doing his job

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Joining bonus = The flat amount of money offered to an employee by a company as an extra incentive for him to leave his previous employer and join them.

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Joint venture = A partnership