In human anatomy the term [defect] means a gap, a space, or a hiatus. It must be clearly understood that the term [defect] does not necessarily mean "defective". There are many defects in the human body which are normal and not defective. An example would be the esophageal hiatus.
This is important to understand in the definition of "hernia" as the presence of a defect can lead to a herniation trough a normal gap in a layer of tissue. It could be argued that since normally there is no hernia, something must have happened to make the defect "defective".