Definition of "indistinguishability"

At times Air Force and CAS efforts blended to the point of indistinguishability.

1991, Earl H. Tilford Jnr, Setup: what the Air Force did in Vietnam and why

But due to the indistinguishability of the particles in the sample, it describes a decay mechanism that occurs for all N atoms simultaneously.

1996 Bose-Einstein Condensation: An Introduction