Dynamic permission definitions allow you to automaticly grant permissions to specifig groups at job creation time. You can define a regular expression to get information from the jobs name. e.g. if all your jobs follow a naming standard, like this: 'group.GROUP.FreeForm', you can define a pattern like 'group.(.*).(.*)' and reuse the regular expression groups in the group format.
e.g.

Job name pattern:	job.([A-Z]{3}).(.*)	this is a regular expression and creates two regex groups: {0} and {1}
Group format:	perm.{0}.Developer	a format to construct a group with, (pattern references (to the groups of the job name pattern) are optional, this allows to define final group names to)
Permissions:		check the permissions you would like the group to have for the newly created job
Job name:	job.ABC.ProjectAJob	the name of the new job
Group assigned:	perm.ABC.Developer	the final group assigend to the job - ABC from got extracted from the job name and used in the group format at the place of {0}. This group will have the selected permissions for the job.