Is there a difference between background and basics when it comes to a thesis, in my case computer science, where the essentials are explained so the reader can understand the implications and argumentation in the following chapters? I am not sure which I should choose; I've seen both, but background is used many times more.
Usually, the "basics" of something means "a simplified overview of something for the benefit of somebody who knows nothing about the subject".
In your case, something like "background" is more appropriate, meaning "the basic information/situation that underpins the arguments/exposé that I will give later on".
Why not just use "Introduction" as a chapter heading?
When I wrote my thesis, that's what we were instructed to call the chapter covering the basics required to understand the following chapters, as well as any background information, including history and reasons as to why the topic was of significance. (The "Introduction" chapter immediately preceded the "Literature Survey"/"Literature Review" chapter.)