Firstly, this is an oxymoron
; and a rather moronic one at that.
What is a church? Well it can be a physical building construct in which church-oriented practices are held, or it can be a term used to refer to the congregation of such a building. On the Internet there are virtual churches in existence which do not have the building but still call themselves a church. So the phrase church can be synonymous with religion, congregation, collective body or any group of individuals who share common beliefs and practices.
So what is a denomination? Well it can be a physical material object that represents a form of currency or weight or other physical property. A dollar bill is a denomination of currency, for example. One in a series of values in a common system. In regards to religion, a denomination represents one in a series of types of religious orders. Each denomination is a large group of relgious congregations which unite under a common faith, and organize themselves under a hierarchy of some sort.
So what is a NONdenominational church?
It is a class of individuals, called by the same name, who co-exist literally or metaphorically under the same spiritual roof, using a name that denotes they do not do such a thing when in fact they do.
Another word for this is hypocrite which is quite common in modern theology.