Do published university admission acceptance rates include applicants for all courses or just undergraduate? Does the acceptance rate of a university is only determined by how many students are applying for undergraduate? Or is it also determined by postgraduate or PhD students?
For example, Harvard has an acceptance rate of 5.2℅, does it also count the grad/phd students?
There is no enforced standard for acceptance rate - it means precisely whatever the institution decides it means (and is generally not audited or required to be made publicly available). It's largely used for marketing of admissions for an institution, so a cynic would point out that the numbers can be assumed to be less than rigorously straight-forward and should not be relied on to be meaningfully interpret-able.

However, generally acceptance rate is by category (undergraduate, Master's, PhD), and is usually defined as applications received compared to student's officially accepted. Some programs have less common relationships between Master's and PhD (such as offering an unfunded Master's to a PhD applicant, and it's unclear if they call that an acceptance or a rejection - but this varies by field). 

Breakdowns in the numbers are sometimes available from some institutions, but you usually have to dig for them. I've seen institutions post acceptance rate of 5-10%, but then deep inspection shows some groups accepted at nearly a 50% rate. Some institutions post enough stats that you can break down by gender, reported race/ethnicity, domestic/foreign, and even give additional info on acceptance (the institution said yes), admittance (the student accepted the offer by the institution), and enrollment (the student actually showed up and started the program). Some provide almost none of this information, and even less institutions provide yearly updates.

Some programs will also give some incredibly limited stats about grades or test scores (average GPA of incoming students, etc - I don't think I've ever seen standard deviations provided).

Finally, as GEdgar pointed out in the comments, some institutions also break up the reporting by department/program (medical school separate from computer science, which is held apart from arts). Sometimes many areas are aggregated together, such as the entirety of the "graduate program" or across colleges, etc. 

In the end, acceptance rate is purely a measure of applications in vs acceptances out. People use it to infer lots of other things, and that's a practice that is extremely questionable - but popular.