ive always known it as stopper, if you have rubbish filler and it leaves loads of holes you can scrape a real thin smear of stopper over it to smooth it out. but tbh you can just do the same with regular filler or just use something decent to start with like u-pol fantastic. last time I used stopper was 20 years ago.
Use a decent filler like upol fantastic and use it as stopper as well if necessary.