A very simple definition of legalism is: adding anything to Salvation.
Among the liberal churches and denominations we of the conservative, Bible-believing and Bible-teaching sort are often called legalists. There is not truth to that statement. You see people who want to live their lives as close to hell as they possibly can without actually slipping or stepping into it call those who make a concerted effort to live the way the Bible tells us we ought to live call us legalists. By the way a lot of them will be surprised where they end up when the die anyway.
In Christ, George
(Galatians 5:1) Stand fast therefore in the liberty wherewith Christ hath made us free, and be not entangled again with the yoke of bondage.