The US Code with its 50 Titles [Title 18 being the Criminal Code] has over 100 definitions of terrorism or relating to it.
The UN still is struggling to define it! See Almost 10 Years After 9/11, U.N. Still Grappling to Define Terrorism
The problem of course is that one person’s terrorist is another’s freedom fighter or insurgent or whatever!
I use a simpler definition: Any person or organization using violence against unarmed persons (innocents) is a terrorist. So you can take or leave my definition. And all religions that don’t clearly renounce expansion by the conduct of a violence against innocents is not in fact a religion but a political belief system.