There are five real forms of the exceptional Lie group, $E_6$. Four of them are notated as in the following:

- The split form as EI or $E_{6(6)}$

- The quasi-split form as EII or $E_{6(2)}$

- EIII or $E_{6(-14)}$

- EIV or $E_{6(-26)}$

What do the annotations to $E_6$ actually indicate and are they also used for real forms for Lie groups in general?