In specialized literature that term "online" is quite often used in the way of description of client-server architecture, and to be more precise it is a client's part.
Client-server architecture is a computing or networking structure in which tasks and network loads are load balanced between network services, or server, and clients who consume those services by giving specialized requests. Client-server communication is often led via the global Internetwork between physical devices and/or software packages.
The client-server technology is by no means considered to be the one of the three pillars of modern global network. Original tasks and purposes meant to serve first are no longer required but that technology gives a great foundation for other more sophisticated tasks and is able of functioning and proceed them properly. One such task is realization of the World Wide Web technology.
The introduction of hypertext documents for constructing of inner informational structure gave huge opportunities in flourishing and mushrooming of different IT systems based on client-server technology. Frankly speaking, our web already constitutes the client-server architecture by means of which one can easily connect to whatever network environment he or she wants with the exception of private and secure networks.
The way we enter the network is only a tip of a great glacier berg, we enter by means of web-browsers using their convenient navigation system and general interface. We request certain information and within a fraction of a second end up with desired results, or the ones which are more preferred on that particular topic. Anyway, we as common users can hardly ever trace the mechanisms that bring us necessary pages and those mechanisms are the greater bottom of the berg, it is constant monitoring and improvement is the problem number one for many digital task forces and IT departments all over the World.
In order to amend and upgrade those mechanisms they were divided into certain layers of data processing. Each layer is responsible for a set of narrow functions, it receives particular piece of information, proceed it accordingly and pass to the next layer down to the recipient or up to the sender. In order to those layers interoperate they are to agree on protocols and interfaces in their narrow sense.
In such a way of data processing and exchange the more advantageous technology is the client-server architecture. That online "request-reply" scheme helps in providing more reliable communication with lesser efforts and functional loads of the bandwidth. At first servers were quite rigid and serve only functional purposes. However, nowadays one and the same piece of memory hardware is capable of functioning as both the client and the server due to expanded technology of multiple bit streams running both sides and widen bandwidth structures which are capable of carrying those streams.