In physics, energy means capacity to do work. Energy may be stored in the most diverse forms in a system. Releasing this energy converts the energy into work. When work takes place, the state of the system changes. Examples of energy are kinetic energy, heat, electrical charge, chemical energy stored in bonds inside molecules, nuclear energy stored in the nuclear forces keeping an atom together and so forth. When energy is released, the system moves from a more organized state into a less organized state, i.e. entropy increases. Burning a log is an example: The energy in the chemical bonds of the wood becomes heat and light which dissipate into the environment and the wood loses structure and becomes ash.
According to special relativity, mass and energy are interchangeable as described by the famous E=mc2 formula. Nuclear reactions convert some of the mass into heat and radiation. Collisions of particles at high energies convert some of the energy into new particles. Other less energetic reactions also follow this formula although there the effect is hardly noticeable.
Information itself is a form of energy because it is contrary to entropy. Anything that deviates from an even distribution of all matter, heat and information can be seen to hold energy in some sense.
The term is often used in a psychological context to denote a person's level of activity.
New Age culture uses this term to refer to both a potential for activity plus a certain mood or flavor or type of intent of this activity. For example 'his energy felt odd that day, it was a weird vibe.'
From an esoteric perspective, energy is all of the above in its different manifestations plus more. Of course, if energy is interchangeable with matter and any phenomenon involving information or order carries a form of energy, there is nothing that is not energy.
But we must distinguish between qualities of energies. We can speak of a whole range of energies, starting wit the forms known to physics. Outside of these, it appears there are increasingly 'intelligent' or 'refined' non-physical energies which may play the role of an ordering principle for 'lower' or 'coarser' forms of energy. These energies are not however directly measurable by physical devices as we understand such.
The Gurdjieffian table of hydrogens may be the most structured classification of these higher substances or energies at least in the publicly known domain. On the other hand, sources like Ra bundle these together under the name of 'intelligent energy' working on 'intelligent infinity.'
In the human domain, each 'center' or area of functioning has its own typical hydrogen or energy. The more refined this is, the more information it carries. This energy may also occur in the context of a group, causing the group to behave more 'intelligently' or 'consciously' than its component members alone would. Sheldrake's idea of morphogenetic field captures a part of this concept.