**Core Concept**
Hernia en glissade, also known as sliding hernia, is a type of hernia where an organ or a part of an organ protrudes through a weakened area in the abdominal wall. This occurs when a portion of the hernia sac is composed of an organ or a part of an organ that normally resides in the abdominal cavity.

**Why the Correct Answer is Right**
In hernia en glissade, the most common content is the colon. This is because the colon is a mobile organ that can easily slide into the hernia sac, especially if there is a weakened area in the abdominal wall. The colon's ability to move and slide into the hernia sac is due to its mesentery, which is a fold of tissue that attaches the colon to the back of the abdominal wall.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because inguinal hernias are a type of hernia, but they are not typically associated with hernia en glissade.
* **Option B:** This option is incorrect because femoral hernias are also a type of hernia, but they are not typically associated with hernia en glissade.
* **Option D:** This option is incorrect because umbilical hernias can occur in infants and adults, but they are not typically associated with hernia en glissade.

**Clinical Pearl / High-Yield Fact**
In hernia en glissade, the presence of an organ or a part of an organ in the hernia sac can make the hernia more difficult to diagnose and treat. Therefore, it is essential to carefully evaluate the contents of the hernia sac during diagnosis and treatment.

**Correct Answer:** C.