What is "GAI" in logic? What is the difference between extension and extension?

Let's talk about extension first: it is a part of the concept, and the concept is the general name of the connotation and extension of things. For example, we say that apple is an edible sweet fruit, and the extension of apple refers to shape, color, quality and so on. The extension of apple includes: big apple, small apple, red apple, good apple, bad apple and so on.

GAI refers to whether the concept we are talking about is endless. For example:

Apples are fruits.

In this sentence, we say that "apples" belong to GAI, because all apples are fruits, no matter whether they are big or small, red or green.