Spectrum of a real number
This is non-standard (and does not agree well with any of the other meanings of "spectrum" in mathematics so I would not use it). The standard name is Beatty sequence (at least when $\alpha$ is irrational).
This is non-standard (and does not agree well with any of the other meanings of "spectrum" in mathematics so I would not use it). The standard name is Beatty sequence (at least when $\alpha$ is irrational).