Late afternoon sun is much stronger and hotter than morning sun. Plants that prefer partial shade will not hold up well if they only receive afternoon sun. The plant may wither, its growth stunted. If we all could have gardens that had east exposures and direct sun from sunrise until noon, we probably would never complain. Or the sun may disappear behind the house at noon.
Full shade means the sun is blocked throughout the day.
In such situations where there is practically no direct sun but where the sun's rays filter through the leaves from time to time. A cheerful shade in strong bright light, such as the north side of a low obstruction which causes a light airy shade, and where one feels the nearness of the sun, or the reflection of the sun from a light-colored building nearby. This is sometimes referred to as reflected light. As you become more familiar with these terms, it will all become much less confusing. Many old-fashioned plants that we know from our childhood grew around the family homestead where there were no trees to obstruct the sun.