Okay kiddo, a quasi-indexical is a word or phrase that can change its meaning depending on the situation or who is saying it.
Let's say you and your friend are playing hide-and-seek. Your friend says, "I'm hiding behind the tree." "I" here is a quasi-indexical because it refers to your friend, not you.
Quasi-indexicals are kind of like magic words that can change their meaning depending on the situation. For example, the word "here" can mean different things depending on where you are.
If you're at home, "here" means your house. If you're at the park, "here" means the park. So the word "here" is a quasi-indexical because its meaning changes depending on where you are.
I hope that makes sense, kiddo!