What beta means
Beta generally refers to faster EEG oscillatory activity above the alpha range. Exact boundaries vary across studies and signal-processing choices.
Why it gets associated with focus
Beta activity appears in many active waking contexts, so popular explanations often reduce it to “focus.” That simplification ignores brain region, task demands and the fact that useful cognition involves interacting rhythms rather than one global frequency.
Beta binaural beats
The PLOS ONE review noted that, among the included entrainment studies, none using beta-frequency stimulation found entrainment effects. That is not a universal verdict on every beta-audio study, but it is a useful caution against guaranteed claims.
Related
Explore binaural beats for focus and the evidence overview.