The nuclear pore complex (NPC) is a large protein complex that regulates component exchange between the nucleus and cytoplasm.
They're basically fusions of the inner and outer nuclear membranes that result in a connecting pore membrane and a "hole" in the nuclear envelope.
Plant cells do, in fact, have nuclear pores.
Nuclear pores can also be seen on all eukaryotic cells.
In the nuclear envelope of a vertebrate cell, there are roughly 1000 nuclear pore complexes (NPCs), however, this number fluctuates depending on cell type and life cycle stage.