Primordial black holes (PBHs) are hypothetical black holes that may have formed soon after the Big Bang, during the early universe. Unlike stellar black holes, which form from the gravitational collapse of massive stars at the end of their life cycles, primordial black holes are thought to have formed from density fluctuations in the very early universe.
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A black hole formed in the early universe rather than as the endpoint of a star. It is not subject to the ordinary stellar-remnant baryon budget in the same way as a black hole formed from a baryonic progenitor. Formation scenarios and observational constraints depend strongly on its mass.