Amusingly, if you insist that we are only allowed to talk in first-order logic, it is impossible for you to talk about the property “finite”, since there is no first-order formula which expresses this property.
An equivalent (and in my opinion less misleading) way of putting this is to say that there’s no first-order formula which expresses the property of being infinite.
An equivalent (and in my opinion less misleading) way of putting this is to say that there’s no first-order formula which expresses the property of being infinite.