TPS, short for Ticks Per Second, is a measure of how fast Minecraft mechanics such as redstone and farming run at. Minecraft runs at a fixed 20.00 TPS. If too many things are happening at once, a server's TPS drops below this value, and causes what players call "server lag" which causes for normal functions of Minecraft to be delayed or to malfunction. Server TPS has been a problem ever since the server was created.
TPS should not be confused with FPS, Frames Per Second, which is the measure of how fast the player's computer is rendering the game of Minecraft entirely, while TPS is usually recognized as the FPS of a server, in which measures the speed of how fast the server renders Minecraft.
Low TPS on 2b2t
The TPS of 2b2t is 20 TPS just after a reset, and usually drops to anywhere between 20 and 10 TPS on a normal day. If the TPS hits 0, the server usually restarts and kicks everyone back to queue (although when the TPS is that low, queue virtually doesn't exist). The TPS of 2b2t has always been terrible, even during its early years.
Bad TPS is caused both maliciously by players and by the inherent limitations of minecraft.
Several different types of Lag Machines have been built for various reasons. It is a well-known fact that the TPS tends to be lower when Youtubers are online, even those native to the server such as Fit or Torogadude, because players who aren't fond of those youtubers will turn on their lag machines in order to make it more difficult for them and their fans to do anything. Generally, the more hated (or feared) the youtuber, the more players turn on their lag machines and the lower the TPS. It is also well-known that generating too many chunks at the same time will also cause a drop in the TPS. Examples of this included the journey Armorsmith made to the End World Border Corner, in which his account kept loading new chunks, which dropped the TPS. 0x22 was also famous for loading new chunks in the Overworld using Elytra causing the server to lag and crash.
Minecraft is not optimized to allow multiple people to play survival minecraft on the same server. It is overwhemlingly single-threaded, meaning that all operations on the server need to happen sequentially on a single core. Even with the overclocked Intel i9-9900K it is running on (June 2019), it can only deal with so much. Compare the ~200 active players on the server with the 10 player limit on Minecraft Realms. Speedhacks aggravate the lag problem by generating of loading multiple chuncks very fast, and just general minecraft things like lighting updates, using redstone, detonating TNT and creating cobblemonsters.
In a nutshell: everthing is delayed or lagged. This makes making things like breaking blocks a pain in the neck without god tools. Even with god tools, low TPS can still be a bit annoying as breaking blocks will cause the phenomena known as a "ghost block" in which a block appears broken and players may go through it, but in reality it is still there and can cause the player to glitch out in it or not allow for block placement near it.
Players "rubber band" when moving, sometimes while riding, but more so when on an entity like a horse or boat. The player moves and then is randomly placed, at any given time, in a sort of limbo where players cannot interact with blocks before being launched back to where the player first began moving before the random occurrence.
Chunks can also stop loading properly. You might find a chunk that will not load, and if you try to enter it, you will slowly fall through the world, and will have to relog to get back to the surface. It is possible to fall millions of blocks into the void by doing this, as while the client believes it is falling into the void, the server believes to you to be on the surface, meaning you won't take void damage.
In conditions of super low TPS, If you are generating new chunks, generated structures such as ponds and plants will generate much later than the actual terrain, meaning you might fall into a hole that opens up beneath you, or have a tree generate on top of you.
The response time and movement speed of mobs are reduced, and damage they may take is delayed. While this has the advantage of making hostile mobs unable to follow players, it also makes passive mobs unable to follow players, even with leads, which makes moving them around pretty impossible. Plus, it takes forever to actually kill anything, passive or not. Damaging other players in PvP is more difficult for the same reasons.
The speed of the day and night cycle is also influenced, as the server has trouble keeping up with the in-game time. This makes the sun and the moon rubberband in the sky.
When the server reaches TPS below 1, caused by powerful lag machines such as Armorsmith's Carolina series, the server will crash, kicking everybody out, and dropping the player count.
Players on 2b have varying opinions on TPS. Some think that surviving the TPS of 2b2t is a rite of passage, and that only true players of 2b can withstand the annoyance of lag and continue to play through it. Others complain and joke about it, calling Hausemaster a lazy for not fixing the lag. Several oldfags claim that they have become used to the bad TPS and have accepted it to be a normal part of 2b2t, while several newfags complain in chat and call the server a slow piece of shit that is barely playable. Players of 2b usually joke about bad TPS being something that weeds out the worst players.
Sometimes it so bad that it can even render the server "unplayable" and can cause an uproar in chat with a torrent of messages complaining about the lag. Notable example to low TPS occurred on the instances when TheCampingRusher joined the server after Fit defeated him in their duel, and on June 1st, 2017. In both cases, everyone turned all their lag machines on in order to prevent Youtubers from being able to do anything.
The most extreme examples of low TPS (so far) was during 2017, a time in which Hausemaster didn't care about lag machines being turned on. It allowed the creation of huge lag machines by players like Armorsmith and househousehouse1 who kept them turned on for hours every single day for weeks. The TPS was so low that it was virtually impossible to even move, chunks would generally not even load, and the chat would sometimes not work.