The Germans have adopted a huge number of (American) English words and phrase since the end of WW II. So far, so good.
But, as the Germans were kind of exorcized of being German, they felt more "cool" to replace German phrase with (American) English ones, and that translated literally. Hence, denglish isn't necessarily the pure absorbtion of (American) English.
E.g., the "translation" of "to make sense" (Sinn machen), which, in German comprehension, doesn't make sense, as nothing can "make" sense rather than to "have" sense (Sinn haben, sinnvoll sein).
Another example is "at the end of the day" (am Ende des Tages), actually meaning "finally", but literally translated into German means the end of the business day. Many Germans use expressions like that without thinking it over.
Another definition of denglish is, of course, influenced by advertising companies, who created slogans like "Come in and find out" (for a perfumery) which suggests to escape from the shop like from a maze. "Powered by emotion" (for a TV channel) is another curious example, because many people took that as "Kraft durch Freude", which was a nazi slogan for their recreation tours organized by the nazi party.
A third and most annoying meaning is the "creation" of english-sounding words which don't exist, at least with that meaning, in English. Primarily, the Germans say "handy" for their cell phones / mobile phones. Just because it sounds so "kool" and because it ain't German.
A: Wir sollten dieses statt jenem machen. (We should do this instead of that)
B: Ja klar, das macht ja auch Sinn! (Yo man, it makes sense)
A: Am Ende des Tages sollte es kein Risiko darstellen. (At the end of the day, it should be no risk)
B: Kewl, schon um fünf! (Kewl, no risk after 5 pm)
A: War eben bei Douglas (the perfumery advertising with "Come in and find out"). Hab wieder rausgefunden! (I got to Douglas and, amazingly, escaped!
B: Alter, so geil! (You're so fly!)
A. Ey du Sack, ich hab neues Handy! (Yo man, I've got a new cell phone)