X-linked dominant is one of the possible ways that genetic traits can be inherited. This pattern is similar to autosomal dominant inheritance in that 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). However, since in this case the gene is located in the X chromosome (men only have one X chromosome, while women have two X chromosomes), the gender of the affected parent play a significant role in the inheritance pattern among sons and daughters.
If the mother is affected by a X-linked dominant disease, all the children will have a 50% chance of inheriting the disorder, being it equally transmitted to sons and daughters (figure 1). However, if the father is the one affected, he will transmit the disorder to all his daughters but to none of his sons, this is explained in figure 2.
If you want to read about the X-linked dominant inheritance pattern in Spanish, you can follow the link herencia ligada al cromosoma X dominante.