What are incoming and outgoing properties in Freebase? I know about properties for a given type in a given domain, but I also see incoming and outgoing properties associated with a property. I tried to find documentation for this but couldn't find anything substantial. Does anyone know what these are?
It would help if you provided an example or context to help clarify your question. Properties can be a master or not, which is a little like incoming/outgoing, but I suspect you are actually asking about incoming/outgoing links not properties.
As Philip said, a property is just a typed object in the graph, so the outgoing links have the values for the /type/property properties - expected type (similar to rdf range), uniqueness, what type it belongs to, etc. Incoming links have the given property as it's value or object. For properties, this is often another property as the subject/source, "delegating" to this property (ie reusing this property with a different name in a different type).
Outgoing Links
property target expected type
/type/object/type /type/property
/type/property/schema /people/person
/type/property/expected_type /type/datetime
/type/property/unique true /type/boolean
Incoming Links
source property
/m/0dl8xrg birthDate /type/property/delegated
If we go and look at the source of that incoming link we see that it's the property /base/svocab/person/birthdate which has the corresponding outgoing link delegating to /people/person/date_of_birth
The direction of a link is aligned with the semantics it has, but links can be navigated in either direction.