A more thorough explanation:

Definition: A stepsister is the daughter of one's stepparent.

A stepsister is not related by blood, but rather through marriage. When a person's parent marries someone who has a daughter, that daughter becomes their stepsister. For example, if John's father marries Jane, and Jane has a daughter named Sarah, then Sarah becomes John's stepsister.

It's important to note that a stepsister is different from a sister. A sister is a female who has one parent or both parents in common with another person. A consanguine sister is a sister who has the same father, but a different mother. A half-sister is a sister who has the same father or the same mother, but not both. A sister-german is a full sister; the daughter of both of one's parents. An uterine sister is a sister who has the same mother, but a different father.

Example: When my dad married my stepmom, I gained a stepsister named Emily. Even though we're not related by blood, we still consider each other family.

Explanation: This example illustrates how a person can gain a stepsister through their parent's marriage. The speaker's dad married someone who had a daughter, and that daughter became the speaker's stepsister. Despite not being related by blood, the speaker and their stepsister still consider each other family.