Final answer:
Commas are used around 'Griselda' in the sentence because it's a non-essential appositive that provides extra information about the subject 'my older sister,' and they indicate that this information can be omitted without altering the sentence's meaning.
Step-by-step explanation:
In the sentence "My older sister, Griselda, is going to college in the fall." commas are used around the name Griselda because it is a non-essential or non-restrictive appositive, providing additional information about the subject 'my older sister'.
This is a grammatical feature where extra information that's not necessary to the meaning of the sentence is offset with commas. Including the name Griselda gives more detail about the sister, but the sentence would still be clear without it: "My older sister is going to college in the fall."