"A great number of these mysterious blob-like creatures drifted ashore on the Mediterranean coast. Their name is a contraction of "Grotesque Blob Monster", and is the generally accepted term for similar unidentified organisms that have been found on coasts across the globe. Very little is known about the Globster as well; if they too are the result of a virus infection, what could their original form have been...?"
In the Queen Dido, it is shown that many of the Il Veltro members turned into Globsters as a result of infection with the t-Abyss virus, with many not surviving. However, this is somewhat contradicted by the rest of the game, where human infection with t-Abyss is shown to result in transformation into an Ooze or a Sea Creeper, based on gender, which serve as the "zombies" for Revelations. One possible explanation is that the Veltro terrorists mutated into Globsters as a result of being infected with highly concentrated doses of t-Abyss. An alternative explanation, not necessarily incompatible with the first, is that Oozes can eventually "evolve" or mutate into Globsters, similar to how Zombies can transform first into Crimson Heads and then into Lickers.
The choice of the name "Globster" and their appearance may be a reference to the beach cryptids also known as globsters. These are unidentified corpses which wash up on beaches from time to time, and have describable features.