A person who doesn't have a preference for receiving or giving. One who can enjoy being penetrated, or in penetrating another.
Versatile or being a Switch is simply that they are able to enjoy both aspects of the sexual roles, and experiences. A versatile person really doesn't mean they don't have a preference, simply that they are more willing to play either role, as determined by their partner.
Versatile is also common in BDSM, more commonly known as Switch, which is where the roles of who is in charge, who isn't, simply changes from one to the other.
This is usually also about allowing each person in the partnership, to enjoy the same actions.
Anal penetration is something people enjoy as much as they enjoy doing the penetrating. People who are versatile, willingly engage in both parts of the act, allowing for their partner to experience both sides, as they do.
In BDSM this also occurs, but is referred to as 'switch', though not as frequent as in the more tame sexual relationships.
Versatile people may engage solely in one type of role, based on the partner. In other words, with one, they maybe the bottom, with another they are the top.
Practice (Associated Acts): In some instances, a versatile will have a preference, but will switch roles, due to their relationship with the person. In some instances, it is to satisfy the other's needs, at the expense of their preferences, or simply for a change.
The reversal of roles, can occur within a session, in which at the beginning one is the top, then later on reverts to being the bottom.
Noteworthy: There are some who claim that 'versatile' people are more open to new positions, or simply new facets of having sex. They are more 'open' to at least trying something different.
Those into 'self bondage' are considered to be versatile, as they are both the dominant and the submissive within the sexual act.