What is meant by the term "two radians" ? ?

Radians are another way to measure angles. 

There are 2*pi radians in a full turn so 360 degrees = 2*pi radians 
180 degress = pi radians  
90 degrees = pi/2 radians etc 

Quite often we talk about measures of radians in terms of multiples (or fractions) of pi. 

To convert from degrees to radians you divide by 180 and multiply by pi. 
To convert from radians to degrees you do the reverse and divide by pi and multiply by 360. 

The term "two radians" therefore is the size of an angle. We can think of it in degrees if that makes more sense by converting it as described above. 

2/pi*180 = about 114.6 degrees. 

If you are doing any calculus you should always make sure you use radians for your angles.