sweeping basically refers to the right hand technique on guitar, by sweeping across the strings with the pick. Usually when people use sweeps they play arpeggios.
On bass there are several different approaches to playing these arpeggios. The most common approaches are the Adam Nitti approach, which is done by sweeping down with the thumb, tapping the highest note, than raking back up with the index.
and there's the four finger approach, which can be down by picking out each string with a different finger, either t i m r or i m r p.
You can also play them in a regular two finger style, which I find to be easier sometimes in the middle of songs.
Here's an example, I'll list the right hand fingerings on top, and left hand on the bottom. This is an E major sweep.
the fingers on both hands are labeled t = thumb, i = index, m = middle, r = ring, p = pinky, T = tap
Code:
two finger i i m i i i i
G|-------------13h16p13----------------|
D|----------14-----------14------------|
A|-------14-----------------14---------|
E|-12h16-----------------------16p12---|
i p m m i p i m m p i
thumb/tap/index
t t t t T i i i
G|-------------13h16h21p16p13----------------|
D|----------14-----------------14------------|
A|-------14-----------------------14---------|
E|-12h16-----------------------------16p12---|
i p m m i p p i m m p i
four finger
for this one I'll label the right hand fingers 1 2 3 4, and you can choose whether to use t i m r or i m r p
1 2 3 4 3 2 1
G|-------------13h16p13----------------|
D|----------14-----------14------------|
A|-------14-----------------14---------|
E|-12h16-----------------------16p12---|
i p m m i p i m m p i 
