From Latin solaris "of the sun," from luna sol, the Sun. The Romans called the sun god Sol, which in Greek is Ἠέλιος Helios.
In esotericism, the term solar is generally used in concert with its lunar companion, and this duality can have many implications. In Western esotericism and the writings of, the solar aspect is seen as masculine, warm, and polarized as positive (+), not "good," just the opposite polarity of lunar, which is negative (-).
In Asian mysticism, the solar current is related to Surya, the Sun god.
In esotericism of all types, the solar influence is related to the Absolute Sun, also called Christ, Avalokitesvara, Vishnu, Amitabha, etc. That is why all religions have solar deities, or "sun gods."
Some example uses of the term solar:
1. In general "solar" can indicate something that proceeds consciously guided by conscious acts, as opposed to the automatic, mechanical, lunar processes of nature.
2. In another context, for example within the body, there are lunar and solar currents. Within us, the lunar current is fallen into disgrace and must be restored, while the solar current remains intact.
3. There are solar and lunar religions: a lunar religion faces backwards, looking only at the past, and remains attached to traditions, habits, mechanical rules. A lunar mind is similar. A solar religion is concerned with the present, and lets go of the past.
4. The lunar bodies are the vehicles we receive from nature automatically: the physical body, vital body, and astral-mental body. Since they were made by nature, they must be returned to nature, thus they are not immortal, eternal, thereby illustrating the need to create solar bodies, which transcend the mechanical, lunar laws of nature. Solar bodies are not made by mechanical lunar nature, but by a special, conscious process hidden in all religions but known only to a few.