Solubility can be defined as the ability of a solute (could be solid, liquid or gas) to dissolve in a solvent in order to produce a solution. There are several factors affecting solubility which includes (basically four) temperature, polarity, surface area of solute particles and pressure of gases. Generally, an increase in temperature leads to an increase in the solubility of a solute in a solvent. This is because an increase in temperature will increase the average kinetic energy of molecules in the solution which leads to increase interaction between the solute and solvent particles. There is a general saying of "like dissolve like" when discussing polarity. For example, organic solvents are used to dissolve organic solutes (just as petrol is used to wash grease off hands and surfaces). Hence, when the solute and solvent have the same polarity, solubility occurs easily, otherwise solubility may be difficult or may not even occur. A reduced/smaller surface area of the solute leads to an increase in solubility as this makes it easy for the solute particles to interact easily with the solvent. In gases, an increase in pressure increases the interaction between the gaseous molecules of the solute and the solvent, thus leading to an increased solubility. Pressure does not affect solubility in solids and rarely in liquids.
