• Drought is generally defined as “a deficiency of precipitation over an extended period of time (usually a season or more), resulting in a water shortage.” 
• It is a prolonged dry period in the natural climate cycle that can occur anywhere in the world.
• It is a slow-onset disaster characterized by the lack of precipitation, resulting in a water shortage.
•  A drought can last for months or years or may be declared after as few as 15 days.

Types of Droughts

• Meteorological drought is defined usually on the basis of the degree of dryness (in comparison to some “normal” or average amount) and the duration of the dry period.
• Agricultural drought should be able to account for the variable susceptibility of crops during different stages of crop development, from emergence to maturity.
• Hydrological drought is associated with the effects of periods of precipitation (including snowfall) and shortfalls on surface or subsurface water supply (i.e. streamflow, reservoir and lake levels, and groundwater).
• Socioeconomic drought is associated with the supply and demand of some economic goods with elements of meteorological, hydrological, and agricultural drought.

Source:

1. Wikipedia
2. Drought.gov