What is hardcore music?

It has also been used synonymously to refer to gabber, a style close to hardcore techno, and as an umbrella term to refer to styles that have emerged from hardcore techno including speedcore, terrorcore, breakcore, noizecore, glitchcore and drillcore, and from breakbeat hardcore such as happy hardcore, darkcore, freeform hardcore and trancecore (the latter grouping often being referred to as UK hardcore due to its origins).