We describe here the characteristics of a very frequently-occurring ASL indefinite focus particle, which has not previously been recognized as such. We show that, despite its similarity to the question sign “WHAT”, the particle is distinct from that sign in terms of articulation, function, and distribution. The particle serves to express “uncertainty” in various ways, which can be formalized semantically in terms of a domain-widening effect of the same sort as that proposed for English ‘any’by Kadmon & Landman (1993). Its function is to widen the domain of possibilities under consideration from the typical to include the non-typical as well, along a dimension appropriate in the context.