Dormancy is a survival strategy exhibited by some temperate climate species which enables them to survive winters.
Such species have a biological clock that tells them to slow activity and prepare soft tissues for an onslaught of freezing temperatures. After a normal growing season, dormancy can be brought on by decreasing temperatures and shortened daylength , or delayed by maintaining summer temperatures and daylength.
When a mature seed is placed under favorable conditions and fails to germinate, it is said to be dormant. There are two basic types of dormancy. The first, seed coat dormancy or external dormancy, is caused by the presence of a hard seed covering or seed coat that prevents water and oxygen from reaching and activating the embryo. The second type of dormancy, embryo dormancy or internal dormancy, is caused by a condition of the embryo which prevents germination.
Species that have well-developed dormancy needs can be tricked to some degree, but not fully. For instance, if you give a Japanese maple (Acer palmatum) an eternal summer by bringing it in the house, it will grow continuously for as long as two years. After a maximum period of sustained growth, a temperate climate plant will automatically go dormant no matter what the season or condition. Deciduous plants will lose their leaves, evergreens will curtail all new growth. This is very stressful to the plant and usually fatal. It will be 100% fatal if the plant does not receive the necessary period of cold temperatures required to break the dormancy.