Here's a breakdown:

* Signal molecule: A chemical messenger that carries information from one cell to another.

* Signaling cell: The cell that synthesizes and releases the signal molecule.

* Target cell: The cell that receives the signal molecule and responds to it.

Examples of signaling cells and their signal molecules:

* Neurons (nerve cells) release neurotransmitters to communicate with other neurons or muscle cells.

* Endocrine cells release hormones into the bloodstream to reach target cells in distant parts of the body.

* Immune cells release cytokines to communicate with other immune cells and regulate immune responses.

The process of cell signaling is essential for all living organisms, allowing cells to communicate and coordinate their activities.