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.
UNF stands for Unified National Fine. It is a common imperial thread type with more threads per axial distance than its UNC 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.