"Center" and "Zentrum" are largely interchangeable when referring to a place where people gather. More often than not, "Center" occurs in compound words, some of which use other English loanwords. Often the result is some kind of pseudo English.

• Fitnesscenter (gym)

• Einkaufscenter (shopping centre)

• Shoppingcenter

• Jobcenter

• Callcenter

• Kundencenter (customer service centre)

There are some cases where you can only use "Zentrum", for instance, in maths or geography.