A synonym for split is heterozygous. Different alleles (alternative variations of a gene) as compared with two copies of the same allele. A lavender bird is genetically lav/lav; a bird split for lavender is Lav+/lav; and a bird who is not lavender is Lav+/Lav+ In this situation there is not appearance difference between a not-lavender and a split.
In other cases, such as silver/gold, there is a difference in appearance between splits and non-splits. Just to be confusing, the split version of silver/gold is called golden:
Silver is S/S
Golden is S/s+
Gold is s+/s+
In other cases, such as silver/gold, there is a difference in appearance between splits and non-splits. Just to be confusing, the split version of silver/gold is called golden:
Silver is S/S
Golden is S/s+
Gold is s+/s+