Outlander means that the character is not native to Yurenth. They can be called Aliens.
When a native of Yurenth leaves the realm for the first time, or when an offworlder comes to Yurenth for the first time, they will get a bad rash on there face. Eventually it will manifest as scab, and when healed- a clear brand. as if they were burned with iron. This Brand is impossible to hide, and almost any Rifter would recognize the Yurenth Brand. When a native comes back the realm the brand disappears, and when a rifter leaves Yurenth they also are healed.
Most realms have some version of the Brand, and they all have subtle effects for native/non-native characters. Yurenth has some interesting effects. One is that all non-native characters have a feeling in the back of your there head that lets them know that they do not belong in Yurenth. And Yurenth natives in the rift feel an especially strong yearning for homerealm.
Also Yurenth Brand brings with is a vulnerability to Cold Wrought Iron.
Most Outlanders are from other realms, but many are from the middle places between the realms.