I'm going to post a series of explanations/descriptions regarding Vajrayana. Please feel free to ask questions!
Vajrayana originated in India and was taught by the Buddha at different times and places. Nowadays it is mostly associated with Tibetan Buddhism. 'Vajra' refers to the indestructible weapon of Indra, king of the gods, which can destroy anything, but cannot itself be destroyed. It symbolises the indestructible quality of the true nature of mind that, once awakened, overcomes all obstacles and defilements. Vajrayana is a specialised part of the Mahayana and uses a variety of different methods to bring about rapid progress towards enlightenment. These special methods are found in the tantras, which Vajrayana relies upon, as distinct from the sutras, which are the basis of the Hinayana and Mahayana paths.
The bridge between the sutras and tantras is the teaching on Buddha Nature, which is the heart of the Vajrayana path. It represents the Third Turning of the Wheel of Dharma, the third main stage of the Buddha's teaching. Previously we saw that there is no self and that phenomena are empty of separate existence in that everything arises in dependence upon many other things. The teachings of Buddha Nature go further and point out that the true nature of emptiness is radiant clarity. Just as sunshine streams out from the sun, so too do the qualities of limitless wisdom and compassion radiate out from the empty nature of all phenomena.
According to this teaching every living being is endowed with Buddha Nature, the potential for enlightenment. Each one of us is inherently pure and naturally perfect and has the capacity for developing limitless wisdom and compassion. This purity and perfection cannot be damaged or destroyed in any way. It is a great freedom and joy that is already complete within us, without the need to add or remove anything.
The problem lies in the fact that most people are unable to recognize this true state of being. It is hidden from us behind the repetitive patterns of our mind which we identify with. For instance, we tend to deal with life by becoming very caught up in the concepts of 'I' and 'me'. This limits us, because once we start identifying with 'me' and fixating on this idea, everything around us starts to divide up into two sides: 'me' and 'you'; 'what I like' and 'what I don't like' and so forth. We completely lose track of the essential wholeness of ourselves and our deep connection to all of life around us - and this obscures our Buddha Nature.
In spiritual texts, Buddha Nature is sometimes referred to as a precious treasure hidden beneath a pauper's dwelling. We act like a pauper unaware of the treasure hidden just beneath the level of our everyday awareness. The Vajrayana path instils confidence in the fact that this treasure is really present within our everyday experience and it offers skilful practices to clear away the mental confusion and negative tendencies of mind that obscure it.