The tag filtrations has a number of completely different questions. There's a definition in probability theory, as an increasing sequence of $\sigma$-fields. There also appears to be some completely different meaning in homological algebra or some other areas (too far from my own for me to understand).
Is this notion worthy of its own tag in any of these cases? (For probability I don't think filtrations need their own tag; I'd just use stochastic-processes.) If so, a more specific tag should be made and an appropriate wiki written. If not, then perhaps the tag should just be destroyed.