A hexagon bolt, or hex bolt to give it its more common name, is a threaded bolt with a plain shank and hexagon shaped head.
UNC stands for Unified National Coarse. It is a common imperial thread type with less threads per axial distance than its UNF equivalent.
A BZP or bright zinc plated fastener is one which has a thin coating of zinc added during production. This protective coating adds durability by protecting the product against rust or oxidisation.