What is meant by Completion Sequence Group

[plops655]

I am reading the vLLM source code and was interested in the file vllm/sequence.py

Specifically, I am wondering what is meant by completion sequence group in the docstring comment for

class CompletionSequenceGroupOutput(
msgspec.Struct,
omit_defaults=True, # type: ignore[call-arg]
array_like=True): # type: ignore[call-arg]
"""The model output associated with a completion sequence group."""

I know what sequence group is but was not aware of any deeper completion sequence group.