IT stack - what is it? (Reading Comprehension)

[shaharhada]

What is IT stack.
In the article
https://www.redhat.com/en/topics/open-source/what-is-open-source
under How does an open source development model work title
in the sentence
Red Hat developers actively participate in hundreds of open source projects across the IT stack.

 

[popatim]

The scope of all things IT is involved with.