Syrup is the name given to a thick, viscous liquid, containing much dissolved (generally crystalline) matter, but showing little tendency to deposit crystals.

The viscosity arises from the multiple hydrogen bonds between the dissolved sugar, which has many hydroxyl (OH) groups and the water.

The syrup employed for medicinal purposes consists of a concentrated or saturated solution of refined sugar in distilled water. The simple syrup of the British Pharmacopoeia is prepared by adding 1000 gramss of refined sugar to 500 cubic centimetres of boiling distilled water, heating until it is dissolved and subsequently adding boiling distilled water until the weight of the whole is 1500 grams. The specific gravity of the syrup should be 1.33.

Flavoured syrups are made by adding flavouring matter to a simple syrup. For instance, syrupus aromaticus is prepared by adding certain quantities of orange and cinnamon water to simple syrup.

Similarly, medicated syrups are prepared by adding medicaments to, or dissolving them in, the simple syrup.

Golden syrup is the uncrystallizable fluid drained off in the process of obtaining refined crystallized sugar.

Treacle and molasses are syrups obtained in the earlier stages of refining.

Technically and scientifically the term syrup is also employed to denote viscous, generally residual, liquids, containing substances other than sugar in solution.