In genetics, recombination is the process of two organisms exchanging pieces of genetic material. It's through recombination that two brown-eyed parents can end up with a blue-eyed baby.
Recombination is responsible for genetic diversity — in other words, for offspring that aren't just like their parents. It happens at various stages of reproduction, notably during meiosis when chromosomes swap segments of DNA. This science term comes up in chemistry and physics as well, when molecules bond together or ions and electrons are joined. Recombination, "be united again," comes from the Late Latin combinationem, "a joining together two by two."