The basic elements of computer security.
A layman's primer.
This won't help you much as far as keeping your computer secure. It is a very cursory discussion of some of the underlying security technology concepts, for those who might be interested.
There are other ways to categorize and parse computer security elements. These seem to be the most useful and simplest to understand, for the average person. Various computer security functions are accomplished through combinations of these elements.
These basic security elements are Authentication, Authorization, Integrity and Confidentiality.
The simplest case is a password protected file. The password effectively "unlocks" the data for access only to Authenticated/Authorized users.
Much of this is accomplished through various forms of cryptography and mathematical obfuscation. That is another subject entirely.
(Some texts include non-repudiation as a 5th element. Non-repudiation which says that an electronic transaction has been sufficiently vetted so that those involved cannot say, "It wasn't me". I consider this to be a subset of data Integrity.)