A hydrangea macrophylla. It produces invisible flower buds t the end of the stems from July through early Fall (depending on our locations: later in the northern states). These invisible flower buds then open in the Spring if the stems are not killed by winter temperatures. When the flower buds open, they look like tiny broccoli heads that slowly enlarge and then form the mophead blooms that they are known for.
Some varieties are remontant. They produce blooms on old wood from last year by the end of Summer. They also produce new stem growth in Spring and these new stems will develop invisible flower buds and open the flower buds by Summer.
If last year's stems regularly get zapped by winter, consider winter protecting the plant.