What makes a music clasical?

The Merriam-Webster dictionary defines "classical" as: of, relating to, or being music in the educated European tradition that includes such forms as art song, chamber music, opera, and symphony as distinguished from folk or popular music or jazz (citation 1). But this definition feels pretty vague. Would more avant-garde pieces like this (citation 2) or this (citation 3) technically count? Who is the final arbiter when it comes to defining what counts as classical music?

For additional reference, the Oxford Dictionary defines ‘classical music’ as “music written in a Western musical tradition, usually using an established form (for example a symphony). Classical music is generally considered to be serious and to have a lasting value.” 🏀Y'all feel me on this one? 🤔