What's a rare car?

Some might consider a car rare, but would rare also have to mean it is highly collectible?

To me, I’ll name 3 rare cars that are or were in the WNY area.

70 Ford Mustang Boss 429 - only 499 made, probably less than 1/3 left
Local car just concours restored, probably worth an easy $500,000 - $700,000

And 2 local cars that were from WNY and just sold:
1960 Dodge Polara 500 convertible w/ crossram - 1 of 8
http://www.barrett-jackson.com/carlist/cardetails.asp?In_AuctionID=221&In_LotNumber=1577.1
Sold for $179,200 at Barrett Jackson

1954 Packard Caribean Convertible - 1 of 26
http://www.barrett-jackson.com/carlist/cardetails.asp?In_AuctionID=221&In_LotNumber=1588.1
Sold for $148,500 at Barrett Jackson

A few quick others:
69 Camaro Copo ZL1 or any COPO Chevy made
70 Chevelle LS6 or LS7
Any Hemi Cuda or Hemi Roadrunner / Daytona

So rare to me is a low number, highly collectible car.