Informally, an object in our space is simply connected if it consists of one piece and does not have any "holes" that pass all the way through it. For example, neither a doughnut nor a coffee cup (with handle) is simply connected, but a hollow rubber ball is simply connected.
In two dimensions, a circle is not simply connected, but a disk and a line are (not sure how a line is, but ok). Spaces that are connected but not simply connected are called non-simply connected or multiply connected.
Is the sphere the only 3d object that can be a truly connected space?
Or is this more aptly used in 1D spaces?