**Core Concept**
A pseudo cyst is a fluid-filled cavity or sac that forms in a body organ or tissue, often as a result of inflammation, infection, or trauma. This type of cyst is not lined with epithelial cells, unlike a true cyst.

**Why the Correct Answer is Right**
A pseudo cyst typically forms in response to tissue damage or inflammation, leading to the accumulation of fluid within a confined space. This process can occur in various organs, such as the pancreas, liver, or kidneys. For example, a pancreatic pseudo cyst might form after pancreatitis, where the pancreatic tissue becomes inflamed and fluid accumulates in the surrounding tissue.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a true cyst is a fluid-filled sac lined with epithelial cells, which is not the definition of a pseudo cyst.
**Option B:** This option is incorrect because a pseudotumor is a mass of inflammatory tissue that can mimic a true tumor, but it is not a fluid-filled cavity.
**Option C:** This option is incorrect because a abscess is a collection of pus, often caused by infection, but it is not a pseudo cyst.

**Clinical Pearl / High-Yield Fact**
It's essential to distinguish between pseudo cysts and true cysts, as the treatment approaches differ. Pseudo cysts often require drainage or surgical intervention, whereas true cysts may require surgical removal or other treatments.

**Correct Answer:** C.