What's this prominience in the B737?
It's a SATCOM (Satellite COMmunication) antenna. It has several purposes, one of them is internet connection for the passengers.

There are different types and configurations. On some aircraft the antenna is in the front, on some it's in the back, some have two.

(image from http://www.b737.org.uk/latest-2016-04-06.htm)