concentration

Concentration is something of a misnomer for the meditative practice and states of samādhi. The word "concentration" carries connotations of tightness, a narrow focus, filtering things out, effortfully squeezing the mind into a small space, but that's not really it. Seen properly, samādhi is about unification of mind, effortless stability. The object of attention may be small (e.g., sensations of the breath at the tip of the nose) but can equally well be vast (e.g., the totality of awareness, infinitely large as in the formless jhanas). It's not that we're forcing attention onto the object, but more that we're relaxing all construction of things that are not the object.