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diff --git a/51.md b/51.md
index bac1a92..5313cea 100644
--- a/51.md
+++ b/51.md
@@ -60,6 +60,7 @@ Aside from their main identifier, the `"d"` tag, sets can optionally have a `"ti
 | Emoji sets            | 30030 | categorized emoji groups                                                                     | `"emoji"` (see [NIP-30](30.md))                                                     |
 | Release artifact sets | 30063 | group of artifacts of a software release                                                     | `"e"` (kind:1063 [file metadata](94.md) events), `"a"` (software application event) |
 | App curation sets     | 30267 | references to multiple software applications                                                 | `"a"` (software application event)                                                  |
+| Calendar              | 31924 | a set of events categorized in any way                                                       | `"a"` (calendar event event)                                                        |
 | Starter packs         | 39089 | a named set of profiles to be shared around with the goal of being followed together         | `"p"` (pubkeys)                                                                     |
 | Media starter packs   | 39092 | same as above, but specific to multimedia (photos, short video) clients                      | `"p"` (pubkeys)                                                                     |