Originally I thought that chan is for the channel as on tv.

But in Japanese "chan" is term for cute as example cat/kitty-kitten
strangely the English language has no way even to translate that.

Guro is probably grotesque "Gurotesuku" as Japanese people can't spell anything without adding vowels everywhere

from Wikipedia:

Ero guro nansensu, frequently shortened to ero guro or just guro, (エログロ ero-guro) is a literary and artistic movement originating c. 1930 in Japan. Ero guro puts its focus on eroticism, sexual corruption, and decadence. While ero guro is a specific movement, many of its components can be found throughout Japanese history and culture.

The term itself is an example of wasei-eigo, a Japanese combination of English words or abbreviated words: ero from "ero(tic)", guro from "gro(tesque)", and nansensu from "nonsense".

from Urban Dictionary:

"chan," usually used in the plural as "chans," can refer to the large array of English-language websites that were inspired by the japanese imageboard 2channel. The largest and most influential of the "chans" is the popular website 4chan , although there are many other similar websites such as 7chan, 420chan, wakachan, iichan, not4chan, gurochan, fchan, sidechan, renchan, and so on.