Cryptojacking is the act of a hacker having injected a script in a web application which causes that all the website visitors will in their webbrowser (via JavaScript) run cryptocurrency mining on behalf of the hacker.
Cryptojacking is a recent trend (since end of 2017). It attempts to exploit all known "remote code execution" vulnerabilities in order to install a piece of JavaScript in a general web page template which in turn runs cryptocurrency mining logic in the client side. This of course causes CPU and memory resource draining in the client side and "slow website" user experience.
