What is meant by "neutral" oils?
Context would make me more sure, but I expect this is referring to neutral flavor.
If you need oil in something for purposes other than flavor, and want to make sure that the other flavors in the dish aren't affected or obscured, then you'd want a neutral oil. For example, for frying and sauteeing, we rarely use strongly flavored oil. (There's the additional problem that many flavors are destroyed at high heat; many more aromatic oils have lower smoke points.)
Oils like sesame oil, chili oil, and walnut oil are decidedly not neutral. On the other end, oils like canola oil and grapeseed oil are neutral. Close to neutral, there are very mildly-flavored oils like peanut oil. Somewhere more in the middle there are things like olive oil, which has some flavor but isn't overwhelmingly strong.
Note that sometimes there's more than one type of oil from a given source, often a more refined one that's more neutral and a less refined one with more flavor. For example, refined olive oil is quite neutral, but extra-virgin olive oil has plenty of flavor; "regular" peanut oil is fairly refined and mild, but there are also flavorful roasted peanut oils.
Chili oil is usually neutral oil that had chilis steeped in it, though, as opposed to oil pressed from chili pepper seeds or something like that. Whether olive oil is strongly flavored or not would vary a bit, I'd think, as well. I guess this just means it's a somewhat subjective assessment!