A sibling is a brother or sister, someone who shares at least one parent with you. If you have siblings, you grew up in the same family, even if you don't always get along perfectly.

Siblings often know each other in ways friends never will. They see you at your best and worst, share inside jokes from years ago, and remember embarrassing moments you'd rather forget. Two siblings might compete fiercely over the last cookie, then defend each other fiercely when someone outside the family causes trouble.

The word works for many family structures. You might have full siblings (who share both your parents), half-siblings (who share one parent), step-siblings (whose parent married your parent), or adopted siblings. What matters isn't biology but the relationship: growing up together, sharing experiences, and being part of the same family.

Birth order creates different sibling experiences. Older siblings often feel responsible for younger ones and sometimes resent always having to set a good example. Younger siblings might feel bossed around but also protected. Middle children can feel caught between. Only children have no siblings at all, which brings its own advantages and challenges.

The relationships between siblings change over time. Siblings who bicker constantly as children often become close friends as adults, while others grow apart. Many people say their siblings are among the most important people in their lives.