phosphates
A phosphate is what you get when phosphoric acid gives up its protons: the salts and esters built on the phosphate ion, PO4 3-. They are, quietly, among the most important inorganic species for life and industry. Phosphates hold up your skeleton (bone is largely calcium phosphate), carry the genetic code (the backbone of DNA and RNA is a chain of phosphates), and power every cell (ATP, the energy currency, is adenosine with three phosphates strung together).
The phosphate ion itself is a small, symmetric tetrahedron: a central phosphorus with four oxygens at the corners and a 3- charge spread over them by resonance. What makes phosphates so versatile is that they link up. One phosphate can share an oxygen with the next, forming P-O-P bridges, to give diphosphate (pyrophosphate, P2O7 4-), triphosphate, and long polyphosphate chains and rings. These P-O-P linkages store usable chemical energy; ATP works because snapping off a terminal phosphate releases energy the cell can spend. In water, phosphate exists as a family of related species (PO4 3-, HPO4 2-, H2PO4-, H3PO4) whose proportions shift with pH, which is exactly why phosphate is the body's main intracellular buffer, holding blood and cell fluids near neutral.
Phosphates dominate real-world chemistry far beyond biology. They are the active ingredient of phosphate fertilisers (most mined phosphate rock ends up here), water softeners, fire retardants, food additives, and detergents — although phosphates in detergents were heavily cut back because phosphate runoff fertilises algae and causes eutrophication, choking lakes and rivers of oxygen. So phosphate is a textbook case of the same molecule being indispensable to life and a serious pollutant when over-released.
Every time a muscle contracts, ATP loses a terminal phosphate to become ADP, releasing the energy that powers the movement — the same P-O-P chemistry that, scaled up, makes polyphosphates useful in water treatment.
The phosphate bond is life's rechargeable battery.
The cell does not store energy in some mystical "high-energy bond"; the energy released when ATP loses a phosphate comes from the whole reaction — more stable products, resonance and charge relief in the freed phosphate — not from a special bond breaking.