We should have an updated thread of all the usual abreviations here... One exists that I know of but it likely doesn't have bunch of things that keep on being thrown around here.
HRT is hormone replacement therapy. In this case a feminising one at it. HGH is human growth hormone, IGF-1 is insulin like growth factor 1, both are extremely important parts of the hormonal trickery that makes breasts grow.
You obviously know what vitamin D3 is?

MSM is Methylsulfonylmethane, Calcium Citrate is self explanatory. These three together affect growth hormone and growth factors in question and this combination is one of the best simplest things to aid boob growth with. This combo comes from Lotus, she has posted about it extensively, but of course all that information is buried in her threads somewhere. This one is a good one, for real, MSM does a thing with growth hormone, D3 in itself is magnificent for IGF-1 levels, these two work fantastically together and it gets better when there's calcium citrate taken with them. Its one of theNBE combos I've been on since before I started HRT and its fantastic. Easily overlooked as it might seem like just some vitamins and supplements together but its one of the silent game changers.
Amino acids might be helpful with HGH levels once again, there are many which human body doesn't produce on its own and they can be easily supplemented. L-tyrosine is one that I like a lot, morning alertness and ease of waking up, plus its beneficial for titty growth. GABA is another but I think its usefulness is somewhat questionable. Then there's L-carnitine & L-ornithine combo I have posted quite a lot about which is potentially one of the best combos for our purposes. Look up my main thread for the article on this subject.
There's more to the amino acids and their combinations, I'm sure its one of the things that need to be studies and tested better, worth looking into.
Also, go thread the topocal cream protocol thread while you're at it. Its likely the single most effective NBE finding for a long time. Eveeryone who has done it correctly for some time seem to be reporting positive changes, often very quickly after starting out. Its definitelyway better than just popping phytoestrogens on their own.

And it seems to pair well with BO and other glandulars.