This image includes the Jenkins build of Spigot, a "modified Minecraft server based on CraftBukkit which provides additional performance optimizations, configuration options and features, whilst still remaining compatible with all existing plugins and consistent with Vanilla Minecraft game mechanics." For more information check the official SpigotMC website.
All available tags are always listed in Docker Hub, the list below explains the maintained tags:
latest,b1235,mc-1.11.2,mc-1.11: Latest server for Minecraft 1.11.x.
Previous builds may also be available as tags in the format b<number>, for
example b1043.