(Under construction; If you have a Vocaloid related question please submit it to the meta thread >>13321)

What is Vocaloid?
Vocaloid is a singing voice synthesizer. It is used to make songs using prerecorded voicebanks.

What is a voicebank?
It is a collection of recorded phonemes that can be used to make speech or singing. Most of them have voice providers who record their voices, but some are completely synthesized.

What about other singing voice synthesizers?
Other software such as UTAU and CeVIO exist.
UTAU is freeware and allows users to use voicebanks that they created themselves.
CeVIO comes in free and commercial versions, and some of its voicebanks allow speech as well as singing.

Do free software or open-source alternatives exist?
Yes. Sinsy is an online Hidden Markov model based singing voice synthesis system. Cadencii and Rocaloid are also worth checking.

What or who is Hatsune Miku?
She is a character/persona created by Crypton Future Media and a Vocaloid voicebank associated with said character. She is also the board's mascot.

What is /miku/?
A board dedicated to Vocaloid, and the characters, songs, culture and works derived from it.

What kind of threads are on /miku/?
We have a Vocaloid news thread, song threads, character threads, comic threads, OC threads, "Upstairs" threads where people chat while posting cute Vocaloids, Miku Monday threads, and many others.

Who is the best Vocaloid?
You're waifu.

Useful links:

Introduction to Vocaloid
Vocaloid Database - http://vocadb.net/
Miku's Recommendations - http://mikurecommends.wikia.com/wiki/Recommended_Albums
Old Miku Monday FAQ - http://pastebin.com/HAZcXajw

Board links: https://8ch.net/miku/links.html