Theism is not a religion, rather it is a belief in god(s). This can be a belief in a single God, as in Islam, Christianity, or Judaism (monotheism), or a belief in deities or multiple gods, such as Hinduism & many ancient religions.
Islam is a type of theism.
Christianity is a type of theism.
Judaism is a type of theism.
Theism can be unrelated to organised religion.
Theism is not the same as religion. Religions can be atheistic, i.e. Buddhism.