Decided to write down all the types anyways.
Type 1. Universes with infinite hubble volumes with hubble volumes identical and unidentical to ours.
Type 2. Universes with spaces that stop expanding and bubbles being the embryo of level 1 multiverses, with potentially different physical constants and etc.
Type 3. Many world interpretation.
Type 4. Modal realism and all possible mathematics.
(Which tries to break down the universe to the most simple language possible.)
I don't know if your refering to the type 4 of tegmark or the type 4 in the 9 types of multiverses though.
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info.
(You can also check the external links.)