What is the term for bacteria that thrive in the absence of free oxygen?

The term for bacteria that thrive in the absence of free oxygen is anaerobic. These organisms have developed mechanisms to grow and obtain energy without utilizing oxygen, which can be toxic to them. Anaerobic bacteria are often found in environments such as deep sediments, gut flora, or other anoxic environments.

The other terms refer to different types of bacteria with varying relationships to oxygen. Aerobic bacteria require oxygen for their survival and growth, as they rely on oxygen to carry out cellular respiration. Facultative aerobic bacteria can grow with or without oxygen, depending on the availability of oxygen in their environment. However, the question specifically asks for bacteria that thrive specifically in the absence of oxygen, making anaerobic the appropriate term.