Regalia is the set of emblems, symbols, or paraphernalia indicative of royal status, as well as rights, prerogatives and privileges enjoyed by a sovereign, regardless of title. The word originally referred to the elaborate formal dress and accessories of a sovereign, but now it also refers to any type of elaborate formal dress. The word stems from the Latin substantivation of the adjective regalis, "regal", itself from rex, "king". It is sometimes used in the singular, regale.
Droit de régale
The term can refer to the rights, prerogatives, and privileges that are held exclusively by any sovereign, regardless of title (emperor, grand duke, etc.). An example of that is the right to mint coins, and especially coins that bear one's own effigy. In many cases, especially in feudal societies and generally weak states, such rights have in time been eroded by grants to, or usurpations by, lesser vassals.
Some emblems, symbols, or paraphernalia possessed by rulers are a visual representation of imperial, royal, or sovereign status. Some are shared with divinities, either to symbolize a god(ess)'s role as, say, king of the Pantheon (e.g. Brahman's scepter) or to allow mortal royalty to resemble, identify with, or link to, a divinity.
The term "crown jewels" is commonly used to refer to regalia items that are designed to lend luster to occasions such as coronations. They feature some combination of precious materials, artistic merit, and symbolic or historical value. Crown jewels may have been designated at the start of a dynasty, accumulated through many years of tradition, or sent as tangible recognition of legitimacy by some leader such as the pope to an emperor or caliph.
Each culture, even each monarchy and dynasty within one culture, may have its own historical traditions, and some even have a specific name for its regalia, or at least for an important subset, such as:
The Honours of Scotland
The Nigerian Royal Regalia
The Three Sacred Treasures of the Emperor of Japan
The Imperial Regalia of the emperors and kings of the Holy Roman Empire
The French Crown Regalia
But some elements occur in many traditions.