I was getting my head around the various formats and products in the Flash Ecosystem.
fla: The typical file format you use to save a project when using adobe flash. This file contains the components of the flash elements that are displayed.
swf: This is a compressed format that is generated from an fla file. An fla file is compiled into an swf and then displayed to the user. To edit the file you would have to edit the fla file. swf stands for Small Web Format.
swc: This is an archive format. These files contain swf files and a catalog.xml along with un-complied files like property files and assets like css. This is usually used to share resources and functionality. You can use a swc from a team member or the internet in your project to use elements in that archive.
Flex is also an IDE used to work on ActionScript intensive projects.