So you have never seen a singlespeed bike? Beach cruisers usually only have 1 speed and they can coast as well. A fixed gear is a bike that has one gear with a fixed hub with a cog and lockring. These bikes cannot coast. However some bikes only have one gear but have the ability to coast. Some bikes have a rear hub with 2 sides, one side has threads for a cog and lockring to ride fixed, while the other side has threads for a freewheel to coast.