What does the term "les Grands" mean in the context of history?

Question

Reading some French texts about historical aspects of France, I have often found the expression "les Grands". For instance, you can read it in this Wikipedia article about the civil wars called the Fronde (emphasis mine):

L'historiographie a pris l'habitude de distinguer plusieurs phases : [...], la seconde à l’opposition des Grands (fronde des princes, 1651-1653).

Another example, from the book La littérature française by Nicole Masson (Éditions Eyrolles), speaking about Jean de La Fontaine's biography (emphasis is always mine):

Mme. de La Sablière décide en 1678 de [...]. La Fontaine vit chez les Grands.

Also in the book Histoire de la littérature française by Xavier Darcos (Hachette) you can read

Du dernier tiers du XVIe siècle au milieu du XVIIe siècle, l'instabilité règne en tous domaines. Politiquement, les Grands sont en conflit ouvert avec la monarchie qui veut unifier et centraliser ; [....].

By the context, I imagine it refers to French nobility. In fact, I have found in the French dictionary Le Robert dictionary that some synonyms of grand used as a noun are noble, aristocrate. But I don't know which is the extent of such term when used in the context of the history of France. Does it exclude the kings? And the fact it's capitalized means that it should be considered as a proper noun? Can anyone explain it?

[Answers in French are welcome.]

Answer 1

Les Grands désigne ici les grands seigneurs, à la tête de fiefs mais qui prêtent serment d'allégeance au Roi de France, ce qui exclut donc ce dernier.

Answer 2

The Grands are also referred to as "grands du royaume" two paragraphs above in that same Wikipedia article.

le pouvoir royal est affaibli par l'organisation d'une période de régence, par une situation financière et fiscale difficile due aux prélèvements nécessaires pour alimenter la guerre de Trente Ans, ainsi que par l'esprit de revanche des grands du royaume subjugués sous la poigne de Richelieu

You will probably get more search engine hits with that idiom.

Their historical importance along the ages of monarchy can be tracked in that other Wikipedia article where they are also called "grands seigneurs", "grands vassaux".

Various sources seem to have "les grands [du royaume]" alternatively capitalized - maybe out of deference, coming from contemporaneous writers - and not capitalized. When used as an adjective ("les grands seigneurs") it is not.