Couples dating is called polyamory. Basically, this means that there are more than 2 people within a relationship. Couples dating can either involve just the just sexual aspect of the relationship, but over time, emotions can develop, making it difficult. Some cultures practice it, but scientific research has shown that most people in polyamorous relationships can be quite unhappy due to jealousy and struggles.
Yes, as Lane64 has put it accurately, couples dating is when a couple have decided to explore relationships with other people, not separately but together. In most cases, the couple is still in love with each other but are just looking for alternative relationship arrangements. While this practice has been going on for many years, it is generally frowned upon by society. Still it is really up to the couple's preferences and what they feel is best for their relationship.
Couples dating is for couples – married or unmarried – who wish to explore sexual relationships with other couples. At one time, such couples were known as “swingers” but the preferred term now is polyamory. Generally speaking, romantic relationships are not part of couples dating, although general attraction may include some romantic flirting. Typically, couples find each other through clubs and private parties, and now they can find one another online through online couples dating sites. In these pairings, all parties have equal say in the relationship, and if it’s not working for one of the four individuals, they have the right to call it quits.