Outcrossing brings together two APBTs that are less related than the average for the breed. By convention both the sire and dam during an outcross should have some linebreeding in their background because no matter how you slice it, breeding a scatterbred dog to a linebred dog produces a scatterbred dog (see our case study below). Many breeders feel this is outcrossing but in reality you now have only half your lines genes and no rational idea what the other half may be. Thus we usually consider outcrossing to involve two linebred or inbred animals from different bloodlines.
A reason to outbreed would be to bring in new traits that your breeding stock does not possess or to decrease the inbreeding coefficient or typically both. When you are looking for high quality traits, also termed aptitudes, that are not present in acceptable members of your germline, then the most obvious way to bring in missing aptitudes is to outcross to a line prepotent for these. Thus, if you are experiencing inbreeding depression you can seek dogs outside your lines with aptitudes that compliment your lines weaknesses. Example one would choose a mate that does not possess the same faults while phenotypically complements and hopefully maintains your dog's good traits. By convention both individuals should be linebred but share no common ancestors in 5 generation pedigree. This promotes more heterozygosity, and gene diversity within each dog by matching pairs of unrelated genes from different ancestors. Note that the key type genes that define our breed will always stay paired. Unfortunately, outbreeding can also mask the expression of recessive genes, and allow their propagation in the carrier state.