Original: The most common form of dashi is a simple broth or stock made by boiling kombu (edible kelp) and kezurikatsuo (shavings of katsuobushi) and then, straining the resultant liquid.
Simplified: The most common form of dashi is a simple broth or stock made by heating kombu (edible kelp) and katsuobushi (flakes of dried skipjack tuna) in water and then straining the resultant liquid.