Over the course of the World Energy Congress, one particular phrase that will be heard a lot will be the "energy trilemma."

Here, CNBC gives you a quick guide to the 'trilemma' and how it can help inform the way we think about the world's energy mix.

The World Energy Council states that its "definition of sustainability is based on three core dimensions."

These 'dimensions' form the WEC's energy trilemma, which is made up of the following:

- Energy security, which encompasses things such as the reliability of infrastructure.

- Energy equity, relating to how accessible and affordable the energy supply is across a population.

- Environmental sustainability, which looks at, among other things, the development of renewable and low carbon sources.

In its most recent World Energy Trilemma Report, the WEC said that the energy sector was "at a transition point" and faced a host of challenges.

The WEC says that its trilemma provides what it says is a "clear framework" to deliver a transformation in energy and make "sustainable energy systems a reality."

Last year's historic COP21 agreement saw global leaders agree to ensure global warming stayed "well below" 2 degrees Celsius and to "pursue efforts" to limit the temperature rise to 1.5 degrees Celsius.

It is within this context that energy security, energy equity and sustainability – the trilemma – will become increasingly important.

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