Second cousins are individuals who share a great-grandparent. When people are second cousins, there are two generations between each of the cousins and their closest shared ancestor.
Second cousins are not the same as cousins once or twice removed. The "removed" term indicates the number of generations that separate the cousins from each other. For instance, a person's second cousin once removed is the parent or child of that person's second cousin. A person's second cousin twice removed is the grandparent or grandchild of that person's second cousin. Understanding these terms can prove helpful at events where many family members will be present, such as reunions or weddings.