User blog comment:Wrath022/Chapter 516: The Truth About Enchantment, Review/@comment-190.58.249.11-20170107175156/@comment-2214433-20170107225849

1. A Person who, being unable to express his anger through physical violence (owning to their physical weakness, lack of bravery and/or conviction in real life), instead manifests said emotions through the text-based medium of the internet, usually in the form of aggressive writing that the Keyboard Warrior would not (for reasons previously mentioned) be able to give form to in real life.

2. The term is a combination of the word 'keyboard' (the main tool by which the person expresses his/her latent rage) and 'warrior' (due to the warrior-like aggression, tendency towards violence, headstrong nature and propensity towards brute force as a means of resolving conflict rather than more subtle means dependant on finesse).

3. The Keyboard Warrior seeks to use the power imbued in his 'weapon' to effect death and destruction (in a strictly-metaphorical sense) upon his foes (other virtual identities he has encountered on the internet). In essence, the keyboard (ie. text input ability) allows the keyboard warrior to manifest his true warrior nature in a safe and removed environment, from which no real-life repercussions.

4. Keyboard Warriors are generally identified by unneccessary rage in their written communications, and are regarded as 'losers' by other virtual identities on the internet.

Thanks urbandictionary

To clarify, I am mostly talking about people from other forums/comment sections.