Between Subject or Between Group
Every person evaluates one solution
A between subject design means that every participant gets to see only one solution during the usability study.
As every participant sees only one solution no direct learning effects can happen within the study itself but therefore it is not easy to compare the evaluation results of the different e.g. prototypes with one another as each participant has a very subjective opinion and does not compare multiple solutions but evaluates only one.
Within Subjects or Repeated Evaluations
A within subject study design requires that every participant evaluates all solutions that are part of the usability study.