Dual Credit is the ability to take Post-Secondary courses while still in high school. Earn 5 30-level credits in high school towards grad requirements and 3 University level course credits for any course you choose. 
These courses, for the most part, are electives in many programs, and can be transferable across many universities and colleges. Being electives is important, as they can be instrumental in one's first year of studies; meaning students may be eligible to take one less course in their first or second year. Being transferable is also important as it allows students to choose where they want to attend their formal program of studies.