Yes, bolus insulin is the fast
🙄 acting insulin you take to cover the food you are going to eat. Corrections are extra units of fast acting
🙄 insulin and can be added to that bolus with a view to bringing your BG back into range if it is high at that premeal reading.... or at other times when not eating to bring levels down into range.
So if your premeal reading was say 10.6 for some reason (as
@Proud to be erratic has explained so well, it is not necessarily a miscalculation on your part from the previous meal but just all the variables which can throw things off) you can add a bit more insulin to the bolus dose to bring you back into range. You would usually be advised to do this once you are more confident and have a correction factor. Without that correction, if you have calculated your bolus correctly, you would still be around that level of 10 four hours later which is still above range, so not ideal.
So for me, I have a correction factor of 2 so for every unit of insulin I inject, it will drop me approx. 2 mmols, so 2 units would drop me 4mmols from 10.6 to a much better in range reading of 6.6, so I would add 2 units to my pre meal bolus injection in that situation and by the next meal I should (hopefully) be nicely back in range..... assuming my basal insulin is holding me steady.
You can also do corrections at other times when not eating but it is generally advised not to do one within 3 hours of a previous injection as that insulin will still be active (this would be referred to as stacking and can result in a hypo) because the insulin still on board may bring you down into range without you needing to inject more.
Hopefully that makes sense, but if not just ask.
PS. I have used rolling eyes emojis after "Fast acting insulin" because even Fiasp isn't exactly "fast" for me.