Just like in English, or every language really, there are different jargons in German. I am using the term jargon here to mean something like "a shared language of specific, well-defined terms among a community of professionals".
Words can mean different things in different jargons. For example, in Stack Overflow jargon, a "poster" is the author of a "post" (question or answer), not a decorative piece of paper you hang on your wall.
In particular, the term you are asking about is from IT jargon, and even more precisely, Microsoft IT jargon.
This particular term is composed of two other jargon terms: Freigabe ("share") and Berechtigung ("permission").
Note that even in English, these two terms are not used exactly with their normal meanings, or their meanings they might have in a different jargon. E.g. a "share" in English IT jargon is something very different from a "share" in English financial jargon. A "share" is "something that is shared by (or to) multiple users". It is "the thing being shared".
How the term "permission" is used, is also slightly unusual. Normally, a permission is something that is granted to someone. It is the active subject that "has" the permission. For example, "I have permission to enter this building". It is me who has the permission, not the building.
However, in IT, we usually talk about an object having a certain set of permissions. E.g. we might say "this file has permissions
0755)". But the file is not the active subject. Instead, when I try to open the file, the Operating System will check whether I "have permission" (in the standard English sense of the term) by looking at what "permissions" (in the IT sense of the term) the file has.
So, in this particular case, the "Freigabe", i.e. the thing being shared is the other person's calendar, and in the process of sharing this calendar to you, the sharer has granted you certain "Berechtigungen". There are different kinds of permissions you can have, from absolutely none (which wouldn't make sense because why would that person share their calendar with you if you then couldn't do anything with it) to only being able to see when that person is free or blocked (but not being able to, see why they are blocked, for example), to also see why they are blocked (e.g. being able to see the titles of their appointments, or even the whole appointment), to being able to schedule meetings with them in their calendar, to even being able to freely move, delete, create, extend, shorten, and edit appointments at will (like an assistant might be doing for their boss).
To summarize, the two most important points to take away are:
- The meaning of compound words does not necessarily have to be the sum of the meanings of their constituent words. (A butterfly is not a fly made out of butter.)
- The meaning of words depends on context (think of "appendix" in literature and medicine, and specifically think about medical literature), in particular, jargon may introduce completely new words, assign new meanings to existing words ("computer" used to be a job title for a human), restrict (while in ancient times, in some sense, a "bookkeeper" was literally someone who kept books, this is not the part of their job that is actually described by this term) or expand the existing meanings of existing words, or any combination thereof.