don't know about vocaloid? do know, but want to read anyway? let's brush up on the basics!
to start, vocaloid is a singing tool first developed for commercial use by yamaha corporation. miku is the face of vocaloid, but she isn't the first! that started with voicebanks leon and lola in english, and meiko and kaito in japanese. they are software that involves a voice actor behind them singing predetermined sounds, which later can be tuned and turned into vocals in a song. the sounds get combined to form whatever words the producer wants it to be. the name vocaloid comes from a portmanteau of "vocal" and "android", as they're singing robots!
because it is an instrument, vocaloid as a musical style is versatile and not defined under one specific label. rock or classical, jazz or pop, offbeat or conventional. there are lots of different sounds, and while the next page may cater to my specific tastes, there are thousands of producers out there in the world in various languages! the japanese scene is the most developed, with musicians such as kenshi yonezu moving on from his vocaloid handle "hachi" to produce original music including openings for various anime (for yonezu, most recently chainsaw man!), but the english scene is steadily gaining recognition through both its producers and youtaites. youtaite?
in japanese, the phrase utaite (歌い手) is a specific word that differentiates itself from the general term for singer, kashu (歌手). it is a term for a person who sings covers and uploads them onto the hosting site nico nico douga. it comes from said cover artists putting utattemita (歌ってみた) in their titles, literally "tried to sing". the english version thus became youtaite, a person who sings vocaloid covers and uploads them to youtube.
as a product, vocaloid is a service that requires you to pay to get a license to use the software, but there are also free offshoots of it, most notably utau. it is a community-built service which has a few built-in voicebanks that differentiate themselves from commercial vocaloids, and many, many community-built voicebanks. yes, utau lets you create and upload your own voicebanks!
while vocaloid updates its software from time to time (we're currently on vocaloid5, launched in 2018), it also originally released in 2004, and as such has a fairly rich history that can be divided into "eras", depending on the most popular producers at the time. being 18 years into its lifespan, there also comes controversy with the idea that vocaloid is a dying artform. the most notable times it has been brought to attention was with hachi's brief return to vocaloid, "sand planet", which depicts the scene as a barren desert, and syudou's response to it, "jackpot sad girl", within the lyrics. ("according to you, it’s too late, for this place has withered and died out already like an anökumene [inhospitable habitat]"...)
to add onto community understanding, many old producers have a "-P" at the end of their name, short for producer, though it's fallen out of major use. the practice stems from the popularity of the series idolm@ster, a game where you play as a producer that trains pop stars. in this practice, it's an honorific given by fans to describe an accomplished artist, usually related to their most popular songs or another characteristic about them. an example is vocaliod-p, who gained his name through often having a typo in his works.