What is Inktober?
Inktober is a daily art challenge during October where artists worldwide participate by sketching and sharing their interpretations of a specific set of prompts. Inktober was created by Jake Parker in 2009 as a challenge to improve his inking skills and develop positive drawing habits. It has since grown into a worldwide endeavor with thousands of artists taking on the challenge every year.
There are now various prompt lists that are available in addition to the Inktober prompts. If you can't find one that appeals to you, go ahead and create your own!
For more information on the Inktober name, trademark and logo, check this page.