The observable physical characteristic of an organism is called its phenotype.

Here's why:

* Phenotype: This refers to the actual, expressed traits of an organism, like its height, eye color, fur color, or disease resistance. These are the features you can see or measure.

* Genotype: This refers to the genetic makeup of an organism, the specific combination of genes it inherits from its parents.

The genotype influences the phenotype, but the phenotype is the result of the interaction between the genotype and the environment.