Abo may refer to:

• ABO blood group system, a human blood type and blood group system
  • ABO (gene), enzyme encoded by the ABO gene that determines the ABO blood group of an individual
• Abo of Tiflis (c.756–786), an Arab East Orthodox Catholic saint
• Adaptive Binary Optimization (ABO), an image compression algorithm
• Indigenous Australians, as the offensive (once casual) term "abo"
• Abo, the anglicized Japanese name for the Pokémon Ekans
• Bankon language, also known as Abo, Abaw, Bo, Bon
• American Board of Ophthalmology, a certifying organization for eye physicians and surgeons (ophthalmologists)
• American Board of Opticianry, a certifying organization for opticians and optical providers

The ABO blood group system is the most important blood type system (or blood group system) in human blood transfusion. The associated anti-A antibodies and anti-B antibodies are usually IgM antibodies, which are usually produced in the first years of life by sensitization to environmental substances such as food, bacteria, and viruses. ABO blood types are also present in some other animals, for example apes such as chimpanzees, bonobos, and gorillas.

Turku (; ) is a city on the southwest coast of Finland at the mouth of the Aura River, in the region of Finland Proper. It is believed to have been first settled around the end of the 13th century, making it the oldest city in Finland. It quickly became the most important city in Finland, a status it retained for hundreds of years. After Finland became part of the Russian Empire (1809), and the capital of the Grand Duchy of Finland was moved to Helsinki (1812), Turku continued to be the most populous city in Finland, until the end of the 1840s. Today it remains a regional capital and an important business and cultural center.