The depiction of at least one character who is the "new sibling" of an individual born of a different family united by marriage.

Simplified version:
S and T were married & V and W were married.

S and T made U.
V and W made X.

Unfortunately, both families divorced.

S remarried someone else, S remarried V.

Since U is the biological child of S... That means that X is the stepsibling of U.

A male (or an intersex equivalent: an andromorph, maleherm) stepsibling is a "stepbrother".
A female (or an intersex equivalent: a gynomorph, herm) stepsibling is a "stepsister".

Stepfamily

• stepsibling
• stepbrother and stepsister
• stepbrother, stepbrothers
• stepsister
• stepparent
• stepfather
• stepfather and stepson
• stepfather and stepdaughter
• stepfather and stepchild
• stepmother
• stepmother and stepson
• stepmother and stepdaughter
• stepmother and stepchild
• stepparent and stepchild
• stepparent and stepson
• stepparent and stepdaughter