Conversion programs resulting in a MSc
In the UK, postgraduate degrees are broken down into two categories Postgraduate Taught (PGT: MSc &amp; MA mostly) and Postgraduate Research (PGR: MRes, MPhil &amp; PhD).
Generally, any 180 credit course for which a Bachelors degree is an entry requirement is referred to as a &quot;master's degree&quot;.
In science, where it is normal to go directly from BSc to PhD without a master's degree, master's degrees generally serve 3 purposes:

To provide more specialist training (often vocational) than is provided in a BSc. For example we have a MSc that qualifies people to work in human genetics diagnostics labs. While were have a module that covers the same general area in our undergrad Genetics degree, this is a whole year of just that very narrow subject. Or alternatively, a student with a computer science undergrad might do a databases masters - the degree title is much narrower than the undergrad equivalent.
To allow people whose Bachelor's degree isn't good enough for what they wish to do in the future to obtain a better qualification. You can often do a PhD in the British system without a masters degree as long as you get a good grade. But PhDs and almost all graduate jobs require good grades (grad jobs require a 2:1 in British speak, and PhDs formally require a 2:1, but you often need a 1st these days). If you don't get the grades you need, you can do a masters degree and have another chance at getting a good grade. The other people who take these sorts of masters are overseas students who want the cache that comes with having a degree from what they regard as a more famous/better regarded university.
Conversion courses. You've a bachelors in one subject, but decide you want to do something different. These degrees will generally have the same title as undergraduate degrees, and often have similar syllabuses, but compressed into 1x180 credits rather than 3x120 credits. These work on the basis that most the teaching at undergraduate level is not the course specific knowledge, but the transferable skills - you learn how to write, how to read, and how to think critically at a high level. Importantly, you also learn how to learn. The assumption is that if you turn this to a new subject, you will learn that new subject much faster than you learnt your first subject. For example, I had a friend who got a 1st class BA in Philosophy, and then did a genetics master's degree.

People in the know (recruiters and PhD admissions panels) will be able to tell what sort of master's degree a particular MSc is. If you have a BA in philosophy, and a MSc in genetics, no one is going to expect you to know as much about molecular cytogenetics as someone with a BA in genetics and MSc in human molecular diagnostics, but if you were both going for a PhD in population genetics, you might be on a similar footing.