ST:TNG: The Borg
By special request, we interrupt our leisurely description of the crew of the NCC 1701-D (or Enterprise-D) to instead skip ahead and explain the Borg.
In the second season of TNG (the episode “Q Who?,” to be precise), Captain Picard boasts to an omnipotent being named Q that his crew is ready to face whatever challenges await them in exploring the galaxy. This annoys Q, so he transports the ship to a distant, uncharted region of space where the crew meets an alien race known as the Borg.
The Borg are cyborgs with pale skin and black or gray cybernetic appendages which they use as specialized tools that give them abilities beyond their organic bodies. They have a hive mind, so they don’t care about individuality or diplomacy; all they want is to assimilate any humanoid life form they come across. (Pretty much all they ever say is “We are Borg. You will be assimilated. Resistance is futile.” And they all chant it in unison.)
An isolated Borg is stronger and smarter than an individual human, because of their cyborg implants. As a hive, the Borg can harness their group intelligence to make decisions instantly and easily outmaneuver their opponents. Basically, the crew of the Enterprise is completely outmatched.
Near the end of the episode, Picard admits to Q that he was wrong and his crew is no match for these alien creatures. Q reappears and graciously moves the Enterprise back to where they originally were, although not before a number of (minor) crew members lose their lives in the Borg attack, plus the Borg have now been made aware of the existence of the Federation, so it is assumed that they will be actively searching for them so they can be assimilated.
The next time the Borg appear is in a 2-part cliffhanger episode in at the end of season 3 / beginning of season 4 of TNG. This time, they kidnap Captain Picard and turn him into a Borg so that he can be a sort of intermediary between the Borg and the Federation. (He got better.) While he was a Borg, he was called Locutus, because the Borg apparently have a thing for quasi-Latinified names (Jean-Luc -> Locutus).
The Borg reappear many more times in the Star Trek franchise, in both TV episodes and movies, but I think this is all the background needed to understand what’s currently going on with the 100 Hour Board.