What is Engineering?

Engineering is the science, discipline, art and profession of acquiring and applying technical, scientific and mathematical knowledge to design and implement materials, structures, machines, devices, systems, and processes that safely realize a desired objective or inventions.
The American Engineers' Council for Professional Development (ECPD, the predecessor of ABET) has defined engineering as follows:

“The creative application of scientific principles to design or develop structures, machines, apparatus, or manufacturing processes, or works utilizing them singly or in combination; or to construct or operate the same with full cognizance of their design; or to forecast their behavior under specific operating conditions; all as respects an intended function, economics of operation and safety to life and property.”

One who practices engineering is called an engineer, and those licensed to do so may have more formal designations such as European Engineer, Professional Engineer, Chartered Engineer, or Incorporated Engineer. The broad discipline of engineering encompasses a range of more specialized subdisciplines, each with a more specific emphasis on certain fields of application and particular areas of technology.

Mainly engineering can be broken down to several branches and disciplines. Although initially an engineer will be trained in a specific discipline, throughout an engineer's career the engineer may become multi-disciplined, having worked in several of the outlined areas. Historically the main Branches of Engineering are categorized as follows:

Aerospace Engineering - The design of aircraft, spacecraft and related topics.

Chemical Engineering - The exploitation of chemical principles in order to carry out large scale chemical processing, as well as designing new speciality materials and fuels.

Civil Engineering - The design and construction of public and private works, such as infrastructure (roads, railways, water supply and treatment etc.), bridges and buildings.

Electrical Engineering - The design of electrical systems, such as transformers, as well as electronic goods.

Mechanical Engineering - The design of physical or mechanical systems, such as engines, powertrains, kinematic chains and vibration isolation equipment.

With the rapid advancement of Technology many new fields are gaining prominence and new branches are developing such as Computer Engineering, Software Engineering, Nanotechnology, Tribology, Molecular engineering, Mechatronics etc.

These new specialties sometimes combine with the traditional fields and form new branches such as Mechanical Engineering and Mechatronics and Electrical and Computer Engineering. A new or emerging area of application will commonly be defined temporarily as a permutation or subset of existing disciplines; there is often gray area as to when a given sub-field becomes large and/or prominent enough to warrant classification as a new "branch." One key indicator of such emergence is when major universities start establishing departments and programs in the new field.

For each of these fields there exists considerable overlap, especially in the areas of the application of sciences to their disciplines such as physics, chemistry and mathematics.

Source: Wikipedia