Definition of "Rare" :

adjective: not widely distributed

"Rare herbs."

adjective: not widely known; especially valued for its uncommonness

"A rare word."

adjective: (of meat) cooked a short time; still red inside

"Rare roast beef."

adjective: recurring only at long intervals

"A rare appearance."

adjective: marked by an uncommon quality; especially superlative or extreme of its kind

"What is so rare as a day in June."

adjective: having low density

"Rare gasses."