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
Jet lag = The dizziness being created by the time difference of long distance flights
Job satisfaction = The satisfaction one gets from doing his job
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.
Joint venture = A partnership