Autosomal dominant is one of the possible ways that genetic traits can be inherited. In this case, the gene is located in one of the 22 autosomal chromosomes and one copy of the altered allele is enough to develop the altered phenotype (orange color in the figures) instead of the normal one (grey color in the figures). You can see in figure 1 how both the genotypes AA and Aa yield the same phenotype and all the children of an AA parent will have the altered phenotype.
Figure 1. Autosomal dominant AA x aa.
If the altered gene version is responsible for a disease, the affected people usually have only one altered allele (Aa), unless both his parents were affected and he inherited two altered alleles, but this is quite infrequent. The children of an affected parent usually have a 50% chance of inheriting the disorder. It is transmitted equally to sons and daughters and the disease is usually present in all the generations of the family as can be seen in figure 2:
Figure 2. Autosomal dominant Aa x aa.
If you want to read about autosomal dominant inheritance pattern in Spanish, you can follow the link herencia autosomica dominante.