Question 5. Atheism, a Religion?

About a year ago, I took a class on world religions. Among the religions were ones you would expect: Christianity, Judaism, Islam, Buddhism, Hinduism, etc. However, my professor spoke that a religion can agnostic, or does not necessarily need to contain a deity. Among the different ideologies my professor mentioned was, curiously enough, Atheism.

Now, Atheism is supposed to be the rejection of any deity, focusing more on explaining the universe through scientific means (or something like that, I could be wrong). In spite of Atheists not believing in a deity, there are those who follow different ideologies (mainly secular) about the universe. Furthermore, Atheism is accepted within some religious belief systems, like Buddhism and Hinduism.

If that's the case, then I have these in mind:

Can Atheism truly be a religion? Why or why not? Furthermore, does an ideology need to have a deity to be called a religion?

Like I said, I do not mean to insult any person of a certain ethnicity or religion. I'm just curious, that's all. If what I stated it wrong, please correct me and explain as to how I can avoid making such mistakes in the future. Thank you.

-Wandering Scholar