On the google analytics where you can see the pie where your traffic is coming from, I have a very small yellow piece that is marked as "other". What is considered "other" traffic?
Other is where Google has been unable to classify the traffic correctly. This could be due to a number of factors including not being able to identify ip subnets correctly or having a garbled response in parameters that are returned to their server.
It really depends. Some of my "other traffic source" is from twitter feeds. You can trace "other traffic source" by going to "traffic sources" on side navigation in Analytics. Then go to "All traffic sources". Go to the dropdown box right beside "Source/Medium" in the middle of the page (should be "none" by default). Then select "Medium" If you sort them, anything that are not "referral", "(none)" and "organic" are your "other traffic source"
Google Analytics offers some great ways to learn about your customer. You may not care which type of web browser your customer uses, but you probably care where your customers live.