The name full nut refers to a standard hexagon nut. They are the most common type of nut and are available in a wide variety of sizes, grades, finishes and thread types.
UNF stands for Unified National Fine. It is a common imperial thread type with more threads per axial distance than its UNC equivalent.
Unified thread types (UNF and UNC) were introduced at the beginning of World War 2 to enable the interchangeability of machinery manufacturing between the USA, Canada and Great Britain. Still commonly found on a vast array of old machines and vehicles in the UK, UNF and UNC threads continue to be the standard thread in the USA and Canada.