Half Races

All the common humanoid races are made from the same template, the same base. As such, interbreeding is possible, if rare. The most common half races are Half-Elves, formed of short (from an elfs perspective) partnerships between an elf and a human or through half elven parents, and Half-Orc, more often than not formed of less savoury pairings. However if one travels the world, one can find other pairings, even very rare ones.
Almost all these are sterile, though typically less than 10% are capable of having mostly fertile children. As such many become drawn to adventuring and other persuits to attempt to leave a legacy.
Most half races have a human as half, they are the majority in most places and interact with most races more than others. The only even slightly common half race that doesnt have a human portion are elphomes, the offspring of a male gnome and a female elf, but it would be odd to find more than one in a population of 1,000 gnomes or elves that live near each other. Half breeds of dwarves are incredibly rare, as dwarves are very unlikely to fall in love with an outsider. Halflings and humans having children is relatively common, but they are not seen as half breeds, more as tall halflings or short humans, and are as fertile as their parents.