A dibling is a slang term used to describe a donor sibling, a person biologically related to someone else through egg, sperm, or embryo donation. It is a portmanteau of the words 'donor' and 'sibling.' The use of the term is not universally accepted in the donor-conceived community. Some individuals feel that it is an easy way to explain a donor-conceived person to young children, while to others the use of cutesy terms is unnecessary and even singles out donor-conceived people as different.
FertilitySmarts explains Dibling
Sperm and egg donors are free to donate numerous times, and often do if they possess qualities that recipients value. This can result in multiple children born in various locations, all with at least one biological parent in common. These donor-conceived people are half-siblings with a common genetic mother (egg donation), father (sperm donation) or full siblings in the case of embryo donation. A donor sibling's genetic information can be useful in identifying genetic traits that a person might otherwise not know about.
The Donor Sibling Registry was created in 2000 in the US, for people who want to know more about their unknown genetic parent. While it sometimes puts donors and biological children in touch, it most often puts donor siblings in touch with each other, as well as their recipient parents. This allows parents to share information and potentially identify any underlying genetic traits their children might have in common. This can be anything from behavioral tendencies to medical issues such as allergies or other, more serious, genetic conditions.