This is the zalgo text generator. It allows you to convert normal text into zalgo text which you can then copy and paste. The zalgo converter engine running behind this translator was made by combatwombat and it allows you to control the height of the zalgo distortions. Simply drag the "craziness level" slider to change how corrupted the text becomes.
Zalgo text is made up of glitchy letters like this: W̶̭̽͆̍͘ḥ̵̢̻̜̐͊a̴̞̭̼̦̞̒̆͒͂͠t̴͍̭̙̪̳́̔͑͠͠͝'̷̹̠̀̒̂̑̀͝ŝ̴̢̬̭̩͠ ̶̙̤̺̃̈́̀͛ù̷̡̞̝̟͍́p̴̛̯͎̯̆͠,̸͖́̍͌́́́ ̷͈̬̖͋͛͆͘t̷̢͍̹͚̰̏͑̂͛͋̐ͅḥ̴̞̄̀͆̉ͅį̶͍̊̐͗ś̶͕̆̒̎͊́ ̷̹̙̽̑i̴̞͑̕s̶͈͛̀̈̀̋̃ ̵̢̛̼̞̱̲̺̒ẓ̴̜͚̺̭̈̒a̴̞͐͗l̴̬̖̦̣̱̯̋̈́̉͒͋̏g̵̛̞̰̟͐̑̆̓͛o̷̻̪͓͒̃͂̽ ̵̛̬̖̎t̴̢̪̭͙̏̌̔ͅe̷̼͕͓͍̦͐̈̎͘͜x̴̲̲͋̂́̅́t̷̩̲̳͐͌.̷̯̟͋̎̏̇̉. It's made up of many unicode diacritic marks the marks on top of words in languages like French and Spanish. Some English words like "cliché" have diacritics (above the "e") because they're inherited from other languages. This zalgo generator, and all others which produce glitchy looking text that you can copy and paste use these diacritic marks to create the weird looking text.
The term "zalgo" comes from an internet meme/phenomenon which begin with the conversion of a Nancy and Archie comic into a sort of demonic scourge beginning to take over the characters (Thus, zalgo text is sometimes called demonic text too). Following this original comic strip in 2004, the meme began to take hold with others posting zalgo comics too.
The term "zalgo" began to be associated with an ominous entity that took over peoples minds, causing insanity and eventually a horrific death. The term "He comes..." and "Nezperdian hive-mind" have come to be associated with the zalgo meme through the comics and an Urban Dictionary entry submitted in 2009.
It has been claimed that the concept of zalgo represents the corruption of innocence, normality and the entire world. Indeed, it has come to symbolise the grotesque decay of normality into a dark and twisted reality through the power of some mysterious evil.
Because of these twisted, evil themes surrounding zalgo, it's often used in any scary or horror-themed context, and is sometimes called "scary text" online when users don't know its origins.
It's also called "glitch text" or "glitchy text" fairly often, and indeed this zalgo-type text may have existed well before the zalgo meme. The name "glitch text" isn't to far from the truth - it's not that there's an actual glitch with the way text is rendered, but it is a sort of "hack" that wasn't really the intention of the people who programmed the text rendering.
The corrupted nature of the text has interesting origins. The story starts with the Unicode statndard; the standards body which governs all the text symbols that you see on all your electronic devices. Unicode needed to design a system which would work for all written languages, and so it had to consider that many languages have a huge number of possible characters because certain "marks" can be added to characters to adjust their meaning. So instead of specifying millions of different characters, Unicode just specified the basic fundamental building blocks plus a bunch of "marks" which can be added to characters. These marks are called "diacritics", and as it turns out, The unicode designers never specified a limit to the number of diacritics that can be added to a character. Someone noticed this and decided to play around with adding many more diacritics than reasonable so that the text became distorted and corrupted. This eventually gave rise to scripts which automatically add the weird marking to letters and eventually to online translators like this one.
The appeal of zalgo text is the fact that it looks like the letters are messed up and the characters are falling apart - sort of like a printing error where characters have been mistakenly repeated or smudged or just printed over the top of one another by mistake. The garbled text and generally corrupted vibe that it gives off makes it a great way to show noobs how good your backing skills are, or to post comments under scary YouTube videos to make people think the world is actually turning into a horror film. This glitch text should work on work on Facebook, Twitter, YouTube, and other social media platforms, just copy and paste it directly to any website that allows you to post text.
Anyway, that's a bit of a rant, but hopefully that gives you an idea of where zalgo text came from and how it works. Feel free to post your zalgo text into the comments section below, and don't forget to try out the "craziness level" slider to adjust the amount of corruption in the resulting zalgo text.