This is a Spanish style of preserving and selling olives, rather than an actual “botanical” variety of olive.
It’s a jar of green olives and capers mixed together. Sometimes the olives may be stuffed with pimiento as well. The olives aren’t necessarily always pitted, though of course they will be if they have been stuffed.
Usually the olives used are Manzanilla olives.
Language Notes
“Alcaparra” in Spanish means “caper”. So, these are “capered” olives.