Wiktionary
vb. (context colloquial English) to exist, or to be available, widespread, possible, or a common practice
Usage examples of "be a thing".
Even the care forced upon them by the sea outside grew in time to be a thing instinctive rather than of thought.
We thought that a detailed, scrupulously truthful record of all we knew, all we had observed from our detachment, might someday be a thing of value to you, even a source of guidance.
You mark my words, giant liners like the Titanic will soon be a thing of the past.
Drizzt hadn't seen the burly man in years and had thought Roddy to be a thing of his distant past.
Beyond the volcanic peak, moreover, the waters seemed to expand into a boundless ocean, and it might be a thing full of risk to be frozen up while the yacht was so inadequately provisioned.