A chalupa is a specialty dish of south-central Mexico.
Traditional chalupas are small, thick, boat-shaped fried dough topped only with Salsa, cheese, and shredded lettuce.
It is made out of flour dough and a thicker kind of shell that is crispy on the outside and soft on the inside.
Though you can use a taco holder for both, traditional tacos tend to be soft-shelled with corn tortillas, and Americanized versions may have crunchy folded shells or wheat tortillas in place of corn.
Chalupas, on the other hand, are rigid and boat-shaped, not folded.
The difference between a Chalupa and a Chimichanga is that chimichanga is (us) a deep-fried wet burrito while chalupa is a specialty food of south-central mexico, consisting of a bowl-shaped fried tortilla stuffed with chopped meat, lettuce, cheese, etc.