In the context of octonions and string theory, $e_i$ refers to the basis elements of the octonion algebra, which are used to represent the eight-dimensional structure of octonions. These basis elements exhibit non-associative properties and play a vital role in encoding geometric and algebraic properties essential for theoretical frameworks in physics, particularly in string theory where they contribute to understanding multidimensional spaces and their symmetries.
congrats on reading the definition of e_i. now let's actually learn it.