What is the difference between electro, electronic, and electronica?

it's rather really selective. best way to get an idea is look at categorizations of artists in each of those genres, or sub-genres. for instance… see what artist iTunes shows you regarding each. this will help you get an idea of what the popular vote is. however, many artists do widen the labeling to increase their exposure.

for me, i relate to electronic music being the main genre, while electronica and electro fall in as subs. essentially my thinking is that "electronic" is such generic definition that the subs help break down the styles. in my ears, "electro" delves into the synthpop, industrial, etc. side of the spectrum- where the instrumental focus is on the non-string elements, sometimes encompassing actual drums over drum machines. while "electronica" takes on a more techno feel. but again, this is all subjective.