Just for thoroughness, however, here is a breakdown of the common post-graduation paths people take to rectify low GPAs, taken from one of my prior posts. My apologies if anything specific to that original post slipped through and is still present:
As a quick overview:
Postbacc: Any undergraduate-level classes taken after graduation from college. These DO affect your AMCAS gpa calculations and can also be seen separately by adcoms (gpas are divided by year: freshman/sophomore/junior/senior/postbacc). This could be one class or many. You can take them piecemeal (DIY or informal postbacc) or as part of an official program (formal postbacc)
Formal Postbacc: A series of undergraduate classes designed for premedical students. Often these include the prerequisites and the programs are intended for career changers - these programs often do not accept students who have taken many med school prereq courses. Others are for GPA repair. These programs are usually 1-2 years long, require application, charge a set tuition (usually very pricy) and rarely have linkage or special consideration from their associated medical school. They affect AMCAS gpa
DIY Postbacc: Any set of undergraduate courses taken after graduation, typically in a pay-by-course fashion, from any combination of schools. This is less structured, requires no application, and never has any sort of linkage, but the scheduling and payment structure can be better for working folks. These also affect AMCAS gpa.
Masters: When used alone, this usually refers to a standard graduate school program. Typically on SDN this will be a research-based grad program, but can also refer to some specialized programs such as MPHs, etc. The GPA from these programs does not affect your AMCAS gpa (though it will be listed separately) and tends to be given low weight by adcoms due to varying rigor across the country and low familiarity (among other things). A low grad GPA can hurt you, but even a great one will not do much to offset poor undergrad performance. Generally the consensus is, do a masters if you would have done it anyway (aside from getting into med) or if it factors into the future career track you are considering in some way. Duration variable; some MPHs are a year, other masters can last several.
SMP: While this is also technically a master's program (special master's program), it is the exception to the rule above: these programs can strongly help offset a low undergrad GPA. It is essentially 'do med school to prove you can do med school'. Often, people will take courses alongside med students. However, do poorly in an SMP and you are basically done. Many of these programs have linkages to their med schools (or at least interview consideration). The price tag, however, is pretty hefty. These are pretty much universally 1yr programs.
As for 'why SMP instead of a masters?', it comes down to the differences explained above, but here are some more details:
Non SMP masters programs don't compensate for a low GPA, and so may have little real effect on your app. Why? Well, for non SMP master's programs, adcoms are not as familiar with interpreting those GPAs as they are uGPAs. I think also that the importance of the actual coursework (and thereby grades) varies widely by program, making it harder to gauge. So while completing a master's program will take time, distancing you from your prior academic shortcomings, and you can demonstrate that hey, you didn't do poorly in the courses you took, it may not do a great job of really showing that you were doing well, either. It's basically all the risk of not doing well with no reward if you do succeed.
More importantly, and I mean this 100%, you should not apply to a graduate program if you would not have done so if med school didn't exist. Getting any sort of graduate degree, especially one in science requires a lot of self-motivation, time, and focus. If it's not something you see yourself doing for the rest of your life, you probably won't be happy doing it, and you probably won't push yourself the way you need to in those programs. And again, it won't even necessarily help your med school application.
The only master's program which does really compensate for a low uGPA is an SMP - a special, expensive program where you take med school classes alongside med students in order to demonstrate that you can perform academically. It's a Hail Mary for the low-gpa applicant...if it works, you can overcome a lot. However, if you don't do exceedingly well, you end up down $50k with a meaningless 'degree' and pretty much zero future shot at medical school. The downfall of the SMP is not just the cost. It's that it is one final, all-or-nothing shot. If you pull a 3.7+, you're in good shape. Less than a 3.5 and you're likely worse off than if you'd never attempted it...and there's nothing that will redeem you from demonstrating directly that no, you can't handle med school coursework. It's generally not something to be undertaken unless your GPA is beyond redemption via normal means. I had a 3.1x after undergrad and I still thought a postbacc was a wiser, cheaper, and more effective route. With a 3.5, it's a completely unnecessary risk.
All of this is academic, however, because the weak point in your application is not even remotely your gpa. It's your ECs. So yeah...maybe take some DIY postbacc courses to bring that gpa up a bit, but only because you need at least a year (if not more) to bring your extracurriculars up to scratch, so you may as well throw in some gpa work if you can handle it (and prevent yourself from getting completely out of touch with being a student.)