Cards are a method of production control, making it easier to track and plan throughout the process. There are a variety of cards, the functions of which sometimes overlap depending upon the production and the preferences of the company producing it. Most of us are familiar with the idea of time cards or library slips; these are a decent analogy, but they tend to contain less detail than a job or route card. Cards do not necessarily have to be physical either.
Route cards are more like guides. They detail the sequence of events and necessary materials for a production, and are more useful for planning than for tracking. A route card does not necessarily mean a particular physical path or direction of travel; we might better describe them as "sequence" cards. They are essentially handed down from someone who has knowledge of the process to someone who is going to actually execute it.
Job cards are a means of tracking what actually takes place in the production process. The job card is created for a single production, and the work and time that goes into that production is then recorded on the card. We might consider the job card to be a demonstration of one or more steps detailed in the route card. This is then used for bookkeeping, payroll, and so forth.