An exoskeleton is a wearable device that augments, enables, assists, or enhances motion, posture, or physical activity through mechanical interaction with and force applied to the user's body.

Other common names for a wearable exoskeleton include exo, exo technology, assistive exoskeleton, and human augmentation exoskeleton. The term exosuit is sometimes used, but typically this refers specifically to a subset of exoskeletons composed largely of soft materials. The term wearable robot is also sometimes used to refer to an exoskeleton, and this does encompass a subset of exoskeletons; however, not all exoskeletons are robotic in nature. Similarly, some but not all exoskeletons can be categorized as bionic devices.

Exoskeletons are also related to orthoses (also called orthotics). Orthoses are devices such as braces and splints that provide physical support to an injured body part, such as a hand, arm, leg, or foot. The definition of exoskeleton and definition of orthosis are partially overlapping, but there is no formal consensus and there is a bit of a gray area in terms of classifying different devices. Some orthoses, such as motorized orthoses, are generally considered to also be exoskeletons. However, simple orthoses such as back braces or splints are generally not considered to be exoskeletons. For some orthoses, experts in the field have differing opinions on whether they are exoskeletons or not.

Exoskeletons are related to, but distinct from, prostheses (also called prosthetics). Prostheses are devices that replace missing biological body parts, such as an arm or a leg. In contrast, exoskeletons assist or enhance existing biological body parts.

Wearable devices or apparel that provide small or negligible amounts of force to the user's body are not considered to be exoskeletons. For instance, clothing and compression garments would not qualify as exoskeletons, nor would wristwatches or wearable devices that vibrate. Well-established, pre-existing categories of such as shoes or footwear are generally not considered to be exoskeletons; however, gray areas exist, and new devices may be developed that span multiple categories or are difficult to classify.

Exoskeletons can serve various purposes related to medical, occupational, or recreational uses and are frequently categorized by their general field of use.

Medical exoskeletons typically serve one or more purposes, such as:

Medical exoskeletons have been designed to support people with certain types of physical disabilities or neurological impairments including stroke, spinal cord injury, cerebral palsy, or limb loss. These exoskeletons can target various specific purposes such as to help balance, ambulation, reaching, grasping, coordination, or other functional movements. For rehabilitation, an exoskeleton may only be used temporarily during a limited period of recovery, after which they may no longer require the device. A rehabilitation exoskeleton can be designed to assist a person with movement impairment, for instance, to help stabilize movement or suppress tremors. Alternatively, an exoskeleton can be designed to resist movement to enhance physical training or to help restore strength. In this case, the exoskeleton is resisting the user in the near-term in order to assist them in recovering strength or capabilities in the longer-term. In either case, exoskeletons can be used to enhance the rehabilitation process by increasing the therapeutic dose (e.g., via increased repetitions or difficulty), constraining exercises to specific movements, reducing the required number of clinicians or clinician effort to provide therapy, or providing assessment of performance through on-board sensing. For assistance, an exoskeleton may be used chronically, intermittently, or only temporarily. Exoskeleton assistance can also be paired with other technologies or modalities, such as functional electrical stimulation (FES) or epidural electrical stimulation (EES).