High-grade glioma is a relatively vague term, and in some ways is best avoided, unless one deliberately wants to be vague/inclusive. It has often (especially in older literature) been used to denote both anaplastic gliomas (WHO CNS grade 3) and glioblastomas (WHO CNS grade 4), always including astrocytomas, but variably also including oligodendrogliomas, oligoastrocytomas, and ependymomas.
In more recent times, its meaning has at times narrowed to refer primarily to glioblastomas, but this is far from universally accepted.
As such it is best, when wanting to be precise, to use WHO classification terminology.