"Money" challenged - and often confounded - economic thinkers for centuries. It functions both as a "medium of exchange" and "unit of account." Simple enough. Too often the focus has been how to use money to stimulate economic activity and achieve political gains. From my perspective, money's importance rests with its fundamental roles as a "Store of Value" and as the bedrock of financial systems. Unsound money has been a root cause of a lot of turmoil throughout history - including the monetary fiasco that collapsed in 2008. Yet concerns for the soundness of contemporary "money" these days are viewed as hopelessly archaic.
My thinking on contemporary "money" has been adapted from a much earlier focus on money's "preciousness." Traditionally, money was precious either because it was made of or backed by gold/precious metals. It retained preciousness only so long as its quantity remained carefully contained. Throughout history, the value of "paper money" has invariably moved inversely to the quantity issued - fits and starts, enthusiasm and revulsion and, too often, a path to worthlessness.