Super Saiyan 5 is the 5th evolution of Saiyans. It has been achieved by few Saiyans in Universe 13, and only one warrior for Universe 14 has achieved Super Saiyan 5.
Super Saiyan 5 is achieved through immense training.
Warriors who have achieved Super Saiyan 5
Currently, Super Saiyan 5 is Chiyo's ultimate form. Super Saiyan 5 was also the strongest form used by many characters in Universe 13 before the Universal Tournament
History of Super Saiyan 5
Ryu after being dead for a year, in Otherworld trained with great fighting masters, and using his own determination, came back to life with the new power of a Super Saiyan 5, an unseen form before this.
When he came back, he eventually taught everyone else the training he went through to achieve the form.