Definition
Hazard labelling is the standard way a chemical product tells you what it can do and how to handle it safely. The label brings together four main elements. Red-bordered hazard pictograms give an at-a-glance signal. A signal word, either Danger or Warning, marks severity. Hazard statements describe the danger itself, and precautionary statements explain how to handle, store and dispose of the product.
H and P statements
Hazard statements, the H-statements, each carry a code and a fixed wording, such as a phrase warning that a product is highly flammable. Precautionary statements, the P-statements, pair with them to say what to do, from keeping a container away from heat to the steps to take after contact. The codes are standardised so the same statement reads consistently across products and languages.
Where the rules come from
The format is set by the CLP Regulation in the EU, which puts the United Nations GHS framework into law. The full set of GHS pictograms is defined there. More detail on hazards and handling appears in the safety data sheet that accompanies many chemical products.
Note: this is general educational information and not legal advice. Check the official source before relying on it.