In biology, "cancer" refers to a group of diseases characterized by uncontrolled cell growth and the ability of these cells to invade and destroy surrounding tissues. This uncontrolled growth leads to the formation of tumors, which can be either benign (non-cancerous) or malignant (cancerous).

Here's a breakdown of key characteristics of cancer:

* Uncontrolled cell growth: Normal cells have a limited lifespan and follow a programmed cycle of growth, division, and death. Cancer cells bypass these controls and continue dividing indefinitely.

* Invasiveness: Cancer cells can break away from the original tumor and spread to other parts of the body through the bloodstream or lymphatic system, a process called metastasis.

* Ability to evade the immune system: Cancer cells can develop mechanisms to avoid detection and destruction by the body's immune system.

The underlying cause of cancer is a mutation in the DNA of a cell. These mutations can be caused by various factors, including:

* Genetics: Some individuals inherit a predisposition to certain cancers from their parents.

* Environmental factors: Exposure to carcinogens (cancer-causing agents) like tobacco smoke, radiation, and certain chemicals can damage DNA and increase cancer risk.

* Lifestyle factors: Diet, exercise, and other lifestyle choices can influence cancer risk.

Understanding the term "cancer" in biology requires recognizing its broad scope and the complex mechanisms involved in its development and progression.