Kilt or a tartan.

[Kid Cossack]

tar·tan (tär'tn)
n.

snip

2. A twilled wool fabric or garment having such a pattern.

So by #2, 'tis both.

Aye, but the SportKilt isn't wool, it's cotton (or a cotton blend) so . . .

Note: just pointing out the definitional issue, not attacking SportKilts. I still think they're great pajamas/pyjamas.