Annadeer,

Perigee (closer)/Apogee (farther) is the astronomical view of planets in conjunction or opposition to the Sun.
For example, Uranus, when Retrograde, is in opposition to the Sun. At the same time, it makes its closest approach to the Earth (called perigee) because the Earth sits in between Uranus and the Sun and making it appear at its brightest.
For Mercury and Venus, this is when they are conjunct the Sun in a retrograde motion (inferior conjunction).

Epstein explains that the planets do not move on a flat Planetary orbits but as spheres within spheres, and when further away from the earth they are reaching higher up towards the heavens. In other words, it is not only about distance from the earth but also about elevation – lower or higher. Thus, a planet in its orbital motion is seen as 'ascending' or 'descending' in its wheels in more than one way.

Also explained in Ibn Ezra in The Beginning of Wisdom Chap.6
'When a planet is 90 degrees away from the beginning of its elevation then it is direct in its motion and the reason is that it is [in an] intermediate [position], and so is its light and the strength of its body. When a planet is less than 90 degrees away from the beginning of its elevation and moving towards it then it is ascending [in the wheel] and decreases in its motion and light and strength of body."
Altitude defined by astronomy is "the angle between the object and the observer's local horizon. For visible objects, it is an angle between 0° and 90°. Azimuth (az.) is the angle of the object around the horizon, usually measured from true north and increasing eastward."

Elevation, low or high of planets can be found in most softwares.
For example, in Planetdance > right-click > Data.

It seems to be an additional way to assess the planetary strength.

Cheers!
Ouranos

thanks a lot Ouranos!