Ok so this is my current understanding, please correct me where I err and supplement where I omit needed information.
Historically the Mensheviks and chartists inspired social democracy whereas the Bolsheviks inspired Marxism-leninism.
They (demsoc and socdem) are extremely similar but have some key differences. Social democrats are to the right of democratic socialists and they are both centre-left parties slightly to the left of social liberalism.
left-ish------Center-left----Center
---------Demsoc-----Socdem Libsoc Lib
Where they differ is usually on imperialism and capitalism.
Social democrats typically support imperialism continuing so long as a slice of the spoils support a welfare state. In that sense they're just capitalist reformists. It also appears that the DSA and the "Democratic-Socialist" movement in the United States is simply social democracy with no intention of seizing the means of production.
Democratic socialists do advocate for seizing the means of production and want the end of imperialism but believe this can be accomplished democratically -- however naive that may be.
As far as I can tell social liberalism appears to be almost synonymous with social democracy but with an added emphasis on the "freedom" to own private property and a more laissez-faire role of the state.
Please fill in my understanding :)
Best answer here.