What does the the German word INGER mean-it is often part of a surname?

Inger is not a German word, regarding surnames it's a suffix.

Family names in Germany developed during the medieval times. At first people had only a first name. In a small village where people knew each other it wasn't much of a problem. But later, when the citys increased and people had to distinguish between ten Peters, they added individual characteristics to the name.

So when one of the Peters was a smith, they called him "Peter the smith", later just "Peter Smith". In that case the person was named after his profession and also his descendants beared that name.

But there were more characteristics than only professions which defined a person's name.

Regarding the suffix "-inger" it's quite possible that the person was named after his or her hometown. Many places in South Germany and Austria have the suffix "-ing". Such as Altoetting. So if someone came from this place, he would be named after it. "Peter from Altoetting" or "Peter the Altoettinger", short: "Peter Altoettinger".

In an English context it would be like "Peter from London", "Peter the Londoner" and the short form "Peter Londoner".

But like I said, mostly towns/townships in South Germany and Austria have the suffix "-ing", accordingly mostly people from there have an "-inger" in their surnames.