When I'm looking at Conversions > Goals > Goal urls some of the goal completion locations says
(entrance). It's not very helpful and I'm wondering why it says that. What does it mean?
This answer to your question sounds identical to this answer for a question on stackoverflow.
"(entrance)" indicates the page which served as an entry point to your site. It could be that when you set up your URL goal, you didn't have any funnel steps, so when a user arrives at your site, they arrive directly at the goal completion URL. It's not something that can be removed. Rather you would just have to add funnel steps to your goal.