This is a frequent question that those of us in the Call Center need to ask customers as we try to accurately place your orders. This can be confusing, especially for parents who haven’t yet had the opportunity to install strings on their student’s instrument. Hopefully the following information will be of help!
Update: Feb 27, 2016 - Removable Ball-End Strings are now a very popular type of Violin E string and Viola A string. These strings have a ball end that can be removed to reveal a loop-end. Not all ball end strings are removable! "Removable Ball" strings will be marked as such, and non-removable ball-end strings will just be listed as "Ball" under End type. - James Engman
The lower three strings (A, D, G for violin or D, G, C for viola) will ALWAYS have ball-ends in the synthetic and steel brands, so you won’t need to worry about those. The E string (or A string, in the case of the viola), however, will either have a loop or a ball end. Some brands have "removable ball" strings. These come with a ball end that can be plucked out to reveal a loop. Cello and Bass strings are always ball end.
A LOOP END looks like this:
... and it attaches to fine tuners that look like this:
A BALL END looks like this:
... and it attaches to the instrument like this:
... or like this:
Note: a loop end string would also work on the above string adjuster; you would simply loop the end over one of the two prongs.
If you have any further concerns about loop vs. ball end, check out these videos: