I was browsing on Movies & TV when this ad came up:
Is this type of ad allowed on a website that's not related at all to trips? I do have an account on Travel.SE but that's all.
Currently it doesn't appear to matter given the state of the ads in place. Anything and pretty much everything, barring porn, seems to be displayed anywhere. That said there does appear to be hope in the future as Terry Guyton-Bradley, a staff member, has repeated they are developing a tool to customise the ad experience. What exactly this is, isn't clear but it sounds like it will mean ads will be targeted better. Whether that's on a site or user level I don't know.
@Robotnik we are developing a tool that will give you control of the ad experience. I dont have a specific date of release, but we are working hard to get it out ASAP.
Thanks for reporting this. This will be removed from our sites immediately. Additionally, we are working really hard to block all inappropriate ads and provide you with reporting and ad customization tool. Again thanks for reporting this ad.
If whatever algorithm happens to think that you might be interested in trips (which could be purely random for all I know), I suppose it's fair game. Having it be related to the page you're on could be a bit constraining as there might not be that many products or services related to Linux's dynamic linker or a question about the acceptability of split infinitives in English.
In the end, it's just someone paying to reach someone who might be interested in what they're selling without wasting money on people who aren't.