Im curious as to thoughts on what makes a kilt a kilt, and at what point does it become just a semi pleated skirt....?

Does material matter? If so, where does that leave synthetics? What about length? While theres some latitude here, at what point about or below the knee does one get outside the realm of the kilt? What about patterns/ colours? Is tartan a must have feature? Where do "modern" utility type kilts fit in- or do they?

I'm curious to see the range of opinions here....