屈指可数 literally means 'bend fingers and can count' — it evokes the image of counting something so few that you only need to bend your fingers (i.e., use one hand) to tally them all. The four characters combine meaningfully: 屈 (to bend), 指 (finger), 可 (can), and 数 (to count). This idiom emphasizes extreme scarcity, not just small quantity — it implies rarity or exceptional exclusivity.

It’s commonly used in formal or literary contexts to describe people, things, or occurrences that are remarkably rare: elite experts in a field, historic milestones, or unique natural phenomena. While it sounds numerical, it functions adjectivally — always modifying a noun (e.g., 屈指可数的专家) and never used predicatively without a copula (e.g., *他屈指可数 is ungrammatical; say 他是屈指可数的专家 instead). It carries a slightly elevated, appreciative tone — suggesting value in rarity, not mere insufficiency.