First-class relics are the physical remains of saints or the attributes identified with them. Examples of attributes would be the key of St. Peter, or the wheel of St. Catherine. 

Second-class relics have only been in existence for around 300 years, and are contact relics (or relics that have been in contact with a saint). 

One example of this is the hand of St Anne shown here. It has a note of contact, which confirms that this wax reproduction was in contact with the actual relic of St. Anne in Vienna on 15 May 1773. Hands of St. Anne were some of the most popular relics, alongside nails from the crucifixion and tongues of St. John of Nepomuk.