Phase and distance describe different things
A Full Moon is a phase: the Moon appears opposite the Sun in Earth’s sky, so its Earth-facing hemisphere is almost fully illuminated. A supermoon adds a distance condition: that Full Moon occurs near perigee, the closer portion of the Moon’s elliptical orbit.
Every supermoon is therefore a Full Moon, but most Full Moons are not supermoons. Because “supermoon” has no single official cutoff, reputable calendars can count a slightly different set in the same year.
Size and brightness
A perigee Full Moon has a larger angular diameter than an apogee Full Moon and sends more light per unit area to an observer. The maximum often-quoted comparison is roughly 14 percent larger in apparent diameter and 30 percent brighter between the closest and farthest extremes.
Those numbers compare opposite ends of the range. Compared with the immediately preceding ordinary Full Moon, the difference is usually subtler. Foreground scale, atmospheric clarity, exposure, and the Moon illusion may influence your impression more strongly.
Tides
Full and new Moons already produce stronger spring tides because lunar and solar tidal forces reinforce one another. When the Moon is also near perigee, the tidal range can be somewhat enhanced. Local coastline shape, water depth, wind, and air pressure still strongly affect observed water levels. A supermoon does not mean a giant ocean wave is moving around the planet.
For observing, treat the label as an invitation to watch a well-timed moonrise, not as a promise that the Moon will look fantastically enlarged.
