Do you know what is Google penalty?

If a website's content conflict with Google's marketing practice then Google punished that particular website it's called as Google penalty which will affect your website SEO rankings.The penalty may come as a result of a latest update of Google's algorithm or the website use "black hat SEO methods ".We all are rely on Search engines for our website traffic. It's necessary to up to date with the latest algorithms.So that we can avoid being subjected to Google penalty and also we can get competitive benefits If we optimize our content according to the latest algorithm updates. But I don't have much knowledge on how to identify a website hit with google penalty or not. Can anyone explain me how to identify whether a website being subjected to google penalty or not?