Creep is development of additional strains in a material over time. Creep is most prevalent under high stressess and temperatures, and is not neccessariliy a failure mode.

Rather than failing suddenly with a fracture, the material permanently strains over a longer period of time until it finally fails. Creep does not happen upon sudden loading but the accumulation of creep strain in longer times causes failure of the material. This makes creep deformation a "time-dependent" deformation of the material.

Creep deformation can be obtained in reasonable time frames under very high temperatures i.e. temperatures around half of the melting temperature. This deformation behaviour is important in system for which high temperatures are endured, such as nuclear power plants, jet engines, heat exchangers etc. Since the relevant temperature is relative to melting point, creep can be seen at relatively low temperatures depending upon the alloy; it occurs at room temperature in solders, and can be seen markedly in older lead hot-water pipes.

Cooling systems of power plants with superheated vapour work under high temperature and high pressure. Or in a jet engine temperatures may reach to 1000 degrees Celsius which may initiate creep deformation in a weak zone. Because of these reasons, understanding and studying creep deformation behaviour of engineering materials is very crucial for public and operational safety.