Trafficking in drugs is an expansive term that includes any activity that involves the manufacture, importation, exportation, distribution or sale of illegal drugs. It also includes possessing drugs if you show the intent or there is evidence that you were conducting any of these activities. Generally, there is an element of earning money from engaging in these pursuits.
Drug dealers whose activities involve enormous quantities of illegal drugs are typically charged with a drug trafficking crime since they are moving them across state or country lines for profit.
Drug smuggling refers to moving controlled substances unlawfully across country or state borders without paying a tax or customs duties, if applicable. Smuggling can be termed as trafficking as it does involve exporting or importing of drugs although there need not be the element of selling or earning money from a smuggling activity.