There is a nomenclature system in naming skin lesions in dermatology. IN this case, the lesions are elevated, sharply defined, less than 0.5 cm in diameter, and filled with serous fluid.
This lesion is called a vesicle.
Primary dermatologic lesions are classified by whether flat or elevated, size (less than or more than 0.5 cm), if it is taller than wide or equal, filled with serous fluid vs. pus etc. Some basic dermatologic lesions are:
Macule - flat lesions less than 0.5 cm
Patch - flat lesions more than 0.5 cm
Papule - elevated lesions less than 0.5 cm
Nodule - elevated lesions more than 0.5 cm
Vesicle - elevated lesions less than 0.5 filled with serous fluid
Bulla - elevated lesions more than 0.5 filled with serous fluid
Pustule - lesions filled with pus