According to the Oxford English Dictionary, the word ubiquitous has two meanings: the first meaning is "(seemingly) present everywhere simultaneously," and the second meaning is "often encountered." Mark D. Weiser, who was a chief scientist at Xerox PARC and is widely considered to be the father of ubiquitous computing, introduced the term, stating that: "it represents a powerful shift in computation, where people live, work, and play in a seamlessly interweaving computing environment. Ubiquitous computing postulates a world where people are surrounded by computing devices and a computing infrastructure that supports us in everything we do."

In ubiquitous computing, individuals will be surrounded by many networked, spontaneously yet tightly cooperating computers, some of them worn or carried, some of them encountered on the move, many of them serving dedicated purposes as part of physical objects, all of them used in an intuitive, hardly noticeable way with limited attention. In other words, ubiquitous computing will truly bring about the era of many computers surrounding a single user and become a transparent part of the physical environment, and its components will be distributed at all scales throughout everyday life and can generally be turned to distinctly quotidian ends.

There are four essential components to ubiquitous computing. The first type of components are wearable devices, which denotes a degree of integration with a piece of clothing or clothing accessory that goes beyond that of mobile computing devices, up to a degree where its computer nature is hardly noticed by the user. There are also customizable sensor nodes which come with a fully programmable microprocessor and micro operating system, a variety of sensor options, and low energy networking. Mass production of these customizable nodes is intended to drive down cost so that easy customization and easy assembly of nodes into sensor networks are set to simplify application development. A third component is networked appliances which are mainly perceived by their users as tools, machines, devices, furniture, and so forth, rather than computers. The fourth is smart labels, which identify physical objects and creatures with an IT-based system.

In a ubiquitous service we can identify the so-called five goals of ubiquity as Availability, Transparency, Seamlessness, Awareness, and Trustworthiness (A.T.S.A.T.). A ubiquitous service should be available anywhere and anytime, which is Availability. Its components should not intrude on the user's consciousness, which implies Transparency, but more than just a user-friendly interface - the technology should facilitate the task in a non-intrusive way and in this way hide the underlying technology from the user. Next, the service should provide an everlasting service session under any connection with any device, or Seamlessness. Its ultimate goal is that the system will recognize the user wherever he or she logs on, on any system, with any equipment, at any time, with the applications in a given state and have them adapt in the best possible way given these surrounding conditions. Ubiquitous devices should extend the human senses by providing greater Awareness of the surrounding environment, through which we should set up mutual awareness between the user-context and the service-feedback. This attribute includes finding out who, what, where, when, and why. Finding out who is the ability of a device to identify not only its owner, but other people and devices in its vicinity within the environment. Finding out what is the ability to interpret user activity and behavior, and using that information to infer what the user wants to do. Finding out where, it follows, is the ability to interpret the location of the user and use that to tailor functionality. Finding out when is the ability to understand the passage of time, use it to understand the activities around it and to make inferences. Finding out why is the ability to understand the reasons behind certain user actions. In addition to the system awareness of its user, a ubiquitous environment provides user feedback for the task in a way that may enhance the user's decisions. Based on the ubiquitous service environment, the service will always behave as expected, which creates Trustworthiness.

Viewing a ubiquitous service from the viewpoint of ubiquitous computing, we shall need the following five criteria (S.C.A.L.E.); Scalability, solutions for huge networks/applications and support for global spontaneous interoperability; Connectivity, intelligent ad hoc cooperation of a multitude of specialized devices over unreliable wireless networks and integration into a meaningful whole based on spontaneous discovery and interaction; Adaptability, adaptation to users and context aware computing to dramatically reduce cognitive load is found in highly adaptive systems that interact optimally with respect to the use case, user, situation, device or resource constraints, and so forth; Liability, security like privacy/traceability tradeoffs, human-understandable trust models, legal binding of service users and providers, and so forth; and Ease-of-use, user friendliness in human-computer interaction as a major concern.

Taking one step forward, the Ubiquitous Healthcare Information System (UHIS) has three objectives, which are to reduce time loss due to lag, reduce the medium cost, and reduce inaccuracy in traditional medical flow. Lag is the time required for printing and sending paper or for human-based transmission of information which causes delays that may represent a major reason for revenue loss. A reduction in lag would reduce the gap between when data is recorded in a system and when it is available for information processing.

In addition, it has to fully realize that events and changes in the real must be reflected in UHIS, and changes and decisions made in UHIS must be forwarded to the real. In other words, ubiquitous healthcare consumers will send out data from various sources, receive real-time medical information, knowledge, and relevant expertise and search out relevant and useful information.

If the above-mentioned criteria are satisfied, UHIS will become truly ubiquitous. It will be a system that is embedded, performing one or a few dedicated functions. It will be pervasive, connecting devices, and embedded in such a way that the connectivity is unobtrusive and always available. It will be context-aware, linking changes in the environment with computer systems. It will be mobile, using technology while moving. It will be wearable, using devices while the user's hands, voice, eyes or attention are actively engaged with the physical environment. It will be sentient, perceiving its environment and reacting accordingly. And it will be ambient, working in concert to support people in carrying out everyday life activities, tasks and rituals in an easy, natural way using information and intelligence that is hidden in the network connecting these devices.