Desire as a noun means a strong feeling of wanting to have something or wishing for something to happen. As a verb it means strongly wish for or want (something). But those definitions are not enough for us to fully comprehend what desire is. So, what is desire?

Lyotard in one of his lectures warn us that when we talk about desire, we have fallen into the habit of examining desire from the point of view of subject and object, the point of view of the duality between desires and what is desired. As a result, the question of desire soon becomes the question of knowing whether it is desirable that arouses desire or the complete opposite, with desire creating the desirable. We need to realize that this way of asking the question falls within the category of causality, that it belongs to a dualist vision of things, and that it thereby makes any serious approach to the question impossible. Desire does not establish a relationship between a cause and an effect.

Desire is the movement of something that goes out toward the other as toward something that it itself lacks. This means that the Other (or the object) is present to what desires, and is present in the form of absence. The movement of desire makes the apparent object appear as something that is already there in desire without however being there ‘in flesh and blood’, and the apparent subject appears as something indefinite, incomplete, which needs the other to define it, to complete it, something that is denied by the Other, by absence.

The essence of desire resides in the structure that combine presence and absence. The combination is not accidental. It is because what is present is absent from itself, or the absent present, that desire exists. Desire is raised into being set up by the absence of presence or the presence of absence. Desire is simply the force that holds presence and absence together without mixing them up.

The domain of the Freudian experience is established within a very different register of relations. Desire is a relation of being to lack. This lack is the lack of being properly speaking. It isn’t the lack of this or that, but lack of being whereby the being exists.
This lack is beyond anything which can represent it. It is only ever represented as a reflection on a veil. The libido, but now no longer as used theoretically as a quantitative quantity, is the name of what animates the deep-seated conflict at the heart of human action….
…. Desire, a function central to all human experience, is the desire for nothing nameable. And at the same time, this desire lies at the origin of every variety of animation. If being were only what it is, there wouldn’t even be room to talk about it. Being comes into existence as an exact function of this lack. Being attains a sense of self in relation to being as a function of this lack, in the experience of desire.
– Lacan, Seminar II, p.223 – 224 (Edited by Jacques-Alain Miller, WW Norton:1991).

Lacan said that the aim of psychoanalysis is to lead the psychoanalyst and/or the patient (the subject) to uncover the truth about their desire, but it is only possible if that desire is articulated or spoken. It is only once it is formulated, named in the presence of the Other, that desire appears in the full sense of the term. So what important is to teach the subject to bring desire into existence.

Lacan differentiate desire with need and demand. Need is a biological instinct that is articulated in demand. Demand represents the way instinctive desires are inevitably alienated through the effects of language on the human condition. Demand has a double function, on one hand it articulates need and on the other acts as a demand for love. So, even after the need articulated in demand is satisfied, the demand for love remains unsatisfied and this leftover is desire. When the need is articulated in demand, there is always a residue of desire. So for Lacan, desire is the difference that results from the substraction of the appetite for satisfaction from the demand for love.

One thing to remember, although in desire there is a relationship between subject and object but it is not so. Desire is not a relation to an object but a relation to a lack (manque), that is the Other. Last but not least, since desire always constituted in a dialectical relationship, it means that desire is a social construct.