NH2 can refer to different chemical entities, depending on the context. Here are some possible meanings:

• Amino radical: NH2 is the chemical formula for the amino radical, also known as the aminyl radical or azanyl radical. It is a highly reactive and short-lived species that forms an important part of nitrogen chemistry. In sufficiently high concentration, amino radicals can dimerize to form hydrazine.
• Azanide: NH2- is the chemical formula for azanide, which is the conjugate base of ammonia (NH3). It is a nucleophilic species that can participate in various chemical reactions.
• Primary amide group: -NH2 is the chemical formula for the primary amide functional group, which consists of a nitrogen atom bonded to two hydrogen atoms and a carbonyl group (-C=O). Primary amides are important building blocks in organic chemistry and biochemistry.
• Hydrazine: NH2NH2 is the chemical formula for hydrazine, a colorless and flammable liquid with a strong odor. It is used as a rocket propellant, a blowing agent for polymer foams, and a precursor to various pharmaceuticals and agrochemicals.

In summary, NH2 can refer to different chemical species depending on the context, such as the amino radical, azanide, primary amide group, or hydrazine.