It can mean all sorts of things. For example, if you had 6 apples, then you ate 3 of them, you would have eaten half the apples you had originally. And half of them would remain.
If you had had 2 apples and then had eaten 1, you would still have eaten half the apples you had. So 3/6 is the same as 1/2, which is the most reduced way of expressing that you had eaten half the apples.
So a fraction is a portion.