A vanilla pod is a whole, long pod of vanilla beans, used in cooking for the flavour that is procured from the beans inside it. (See separate entry on vanilla.)
When buying vanilla pods, look for long, supple ones that are moist and will bend a bit. The colour should be either black and a brown so deep it is almost black.
Though many recipes will call for the pod to be used whole, you will get a more profound flavour from using just the seeds instead.
To get the seeds, cut the Vanilla Pod in half (lengthwise) to expose the seeds. The seeds are the black flecks inside.
Use the point of a knife to scrape them away from the pod. The emptied pod is still good, though — you can put it in a jar or container of sugar where its aroma will flavour the sugar, giving you vanilla sugar.