In one of the cross stitch groups I belong to, a unicorn is that chart or pattern or kit or design that is (usually) out of print or so rare that it's as elusive as a unicorn.
I have several unicorns I'd love to find, and last week I found one:
Fenwick is a kit from Elsa Williams that is probably forty or fifty years old. I always loved the design, but never had the chance to buy it when Elsa Williams products were in existence. But--aha!--it appeared on the Bay of Evil, and I spent way too much for it, but it's now in my possession.
I've always said that if I'm meant to have something, it will eventually come my way--even if it takes decades to arrive!