I can see why you are confused.
the term is actually "the secondary effect of rudder"
ok lets give you a mental word picture to help you.
you are cruising along in straight and level flight, ok.
you pull back the throttle and the aircraft slows down, you trim in a little bit of up elevator to maintain altitude.
ok so you are now flying at a speed well below the manoeuvring speed for the aircraft, that is important for the following.
the centreline of the aircraft is aligned in the direction of flight, everything is in trim and you can take the hands off the controls and the natural stability of the aircraft will keep it flying along just peachy for a while.
ok you hold wings level and very quickly apply a boot full of rudder.
what happens next is that the deflection of the rudder creates air pressure changes to the fin and rudder which causes a force to be applied to the tail of the aircraft. conceptually the force is at the centre of pressure of the fin/rudder and acts horizontally. this horizontal force slews the body of the aircraft about the centre of gravity but the aircraft, at least momentarily, continues along in the original direction.
during this moment the aircraft is flying with one wing a little more forward than the other wing.
a number of things are now changed in regards the wing.
the fuselage will slightly blanket the trailing wing making the forward wing seem slightly longer and thus generate slightly more lift.
as well on wings that have dihedral the forward wing will be at a slightly higher angle of attack than the trailing wing and this will also slightly increase the lift from the forward wing.
you can see this for yourself next time you go flying. slow the aircraft to about 20 knots faster than the stall, get everything trimmed out and stable. then apply a boot full of rudder while looking out along the wing.
the secondary effect of rudder is worth understanding because on a lightie you can use the technique to pick up a dropping wing at the stall.