A Personal Build is a build-out of the common builds sequence and which typically uses the changes not yet committed into the version control. Personal Builds are usually initiated from one of the supported IDEs via the Remote Run procedure.
A Personal Build uses the current VCS repository sources plus the changed files identified during the remote run initiation. The results of a Personal Build can be seen in the "My Changes" view of the corresponding IDE plugin and on the Changes page in TeamCity. Finished Personal Builds are listed in the builds history, but only for the users who initiated them.
Read more about running commits via Remote Run in Pre-Tested (Delayed) Commit.
By default, users only see their own Personal Builds in the builds lists, but this can be changed via the "Show all personal builds" option in My Settings & Tools | General | UI settings of the user profile.
It is possible to restrict running Personal Builds in the General Settings of a build configuration.