I'm a little confused what you are referring too exactly. All the stuff in the filter is called 'filter media'. The biological medium is usually little ceramic pellets or rings. They can be in a mesh bag or just loose. There can be sponge and carbon as well as floss.
It's best not to replace anything in the filter unless it is literally falling apart. It all contains the beneficial bacteria. Carbon doesn't last more than a month so its not necessary and floss can be replaced once its clogged as long as there is plenty of other media to sustain the cycle.