The resources for a project are kept in the repository on a server. When a developer needs to edit these resources (e.g. new development, bug fixing etc) they must checkout the project to get their own local copy of it, called a working copy.

Each developer has their own working copy on their local machine and the changes they make are not visible to other developers until they commit those changes back to the server.

A developer can have multiple working copies on their local machine at one time. Normally they would have at least one working copy for each different project they are working on. However it is also possible to have multiple working copies for the same project when the developer is working on different branches of the same project simultaneously (e.g. bug fixing the current release and developing a new release at the same time).

It is very important to note that Subversion does not support the concept of exclusive file locking by default that some other revision systems offer. All developers have access to the same resources at the same time.