Here's what Wookieepedia says about it:
https://starwars.fandom.com/wiki/Star_Wars_Legends
https://starwars.fandom.com/wiki/Holocron_continuity_database
Official levels of canon
The Holocron continuity database was an internal database maintained by Lucas Licensing for the express purpose of trying to maintain continuity within all licensed products, prior to the April 2014 declaration of a single official canon. This Holocron was sorted into five levels of canon that reflected LFL's canon and continuity policies: G, T, C, S, and N. G, T, C, and S together formed an overall continuity that was considered by Lucasfilm to be the "true" Star Wars canon prior to the decanonization of the Expanded Universe.
The Holocron continuity database was an internal database maintained by Lucas Licensing for the express purpose of trying to maintain continuity within all licensed products, prior to the April 2014 declaration of a single official canon. This Holocron was sorted into five levels of canon that reflected LFL's canon and continuity policies: G, T, C, S, and N. G, T, C, and S together formed an overall continuity that was considered by Lucasfilm to be the "true" Star Wars canon prior to the decanonization of the Expanded Universe.
G (George Lucas) canon was absolute canon. This category included the six films, some of the deleted scenes from the films, the novelizations of the films, the radio dramas based on the films, the film scripts, and any material found in any other source (published or not) that comes directly from George Lucas himself. G canon overruled all other forms of canon when there was a contradiction.
T canon referred to the canon level comprising only the television show Star Wars: The Clone Wars.
C (continuity) canon referred to the main body of EU work, and was the next most authoritative level of canon. All material published under the Star Wars label but not falling into G, S, or N was C canon, and was considered authoritative as long as not contradicted by G canon. Games were a special case as generally only the stories would be C-canon while things like stats and gameplay were N-canon. If the video game had several possible endings or if the player could choose the gender or the species of the main character, only one of each is considered C-canon. C-canon elements have appeared in the movies, thus making them G-canon. These included Coruscant (both its name and the concept of it being an ecumenopolis), swoop bikes, Aayla Secura, YT-2400 freighters, and Action VI transports.
S (secondary) canon referred to older, less accurate, or less coherent EU works, which would not ordinarily fit in the main continuity of G and C canon. Unless referenced by a G- or C-level source, the story itself is considered non-continuity, but the non-contradicting elements were still a canon part of the Star Wars universe. For example, this included The Star Wars Holiday Special, the Marvel comics, the popular online roleplaying game Star Wars Galaxies, and certain elements of a few N-canon stories.
N continuity material is also known as "non-canon" or "non-continuity" material. What-if stories (such as those published under the Infinities label), game stats, "comic" material such as Angry Birds Star Wars or Jedi Academy and anything else that was directly contradicted by higher canon and could not at all fit into continuity was placed into this category. N-canon was the only level that was not at all considered canon by Lucasfilm.
T canon referred to the canon level comprising only the television show Star Wars: The Clone Wars.
C (continuity) canon referred to the main body of EU work, and was the next most authoritative level of canon. All material published under the Star Wars label but not falling into G, S, or N was C canon, and was considered authoritative as long as not contradicted by G canon. Games were a special case as generally only the stories would be C-canon while things like stats and gameplay were N-canon. If the video game had several possible endings or if the player could choose the gender or the species of the main character, only one of each is considered C-canon. C-canon elements have appeared in the movies, thus making them G-canon. These included Coruscant (both its name and the concept of it being an ecumenopolis), swoop bikes, Aayla Secura, YT-2400 freighters, and Action VI transports.
S (secondary) canon referred to older, less accurate, or less coherent EU works, which would not ordinarily fit in the main continuity of G and C canon. Unless referenced by a G- or C-level source, the story itself is considered non-continuity, but the non-contradicting elements were still a canon part of the Star Wars universe. For example, this included The Star Wars Holiday Special, the Marvel comics, the popular online roleplaying game Star Wars Galaxies, and certain elements of a few N-canon stories.
N continuity material is also known as "non-canon" or "non-continuity" material. What-if stories (such as those published under the Infinities label), game stats, "comic" material such as Angry Birds Star Wars or Jedi Academy and anything else that was directly contradicted by higher canon and could not at all fit into continuity was placed into this category. N-canon was the only level that was not at all considered canon by Lucasfilm.
https://starwars.fandom.com/wiki/Star_Wars_Legends
https://starwars.fandom.com/wiki/Holocron_continuity_database
