I agree that much hinges here on definition. I propose the following.
The baptismal vocation is to die and rise in Christ, thus being incorporated into his Body and being given eternal life. Thus Christians all "called" out of darkness into His marvelous light. Living out such a vocation can, however, take many specific forms that are also called vocations.Those in consecrated life are "called" to bind themselves to Christ in a more explicitly visible form that most believers. Clergy and religious are thus meant to represent for the Church what the Church as a whole is meant to represent for the world. Those in married life are also "called" to bind themselves to Christ by making an irrevocable gift of themselves to a particular person. Sacramental marriage thus signifies, and helps to make concrete, the relationship between Christ and his Church. That is not as explciit a sign of Christ as the consecrated state because, outwardly and visibly, it is not as different from what unbelievers do. Hence the term 'vocation' has often been used for consecrated life as opposed to marriage: the consecrated are called out of the ordinary course, i.e. marriage, to something more visibly and objectively Christlike.
Both consecrated and married life are "avowed" forms of vocation: they are constituted by specific promises. As such, they are recognizable forms of the baptismal vocation. By contrast, those who are called to neither consecrated nor married life have total flexibility in answering the baptismal vocation. There are no "vows" specifying for them what form the answer is to take. So we might define the "single" vocation as simply the Christian vocation unspecified by vows.
