Display is a form of animal behaviour, linked to survival of the species in various ways.
One function of display is in courtship. In most species the male has a striking feature that is distinguished by colour, shape or size, used to attract a female. In many species the male has another, more cryptic, form out of the mating season.
A related function is armament (horns, teeth) exhibited and used by 'tournament' species. In these species, males fight to gain the 'right' to breed. The display part of the process is a mechanism for younger males to avoid being damaged by prime males. Instinctive behaviour prompts lesser males to leave the field. Peafowl, deer, antelope and elephant seals are good examples.
The other main function is in species which have territorial display behaviour. This may preserve a foraging or hunting territory for its family or group.