The general use of the word, as is so often the case, is rather inaccurate. Ingram says:
Careless or rhetorical writers use the words "slave" and "slavery" in a very lax way. Thus, when protesting against the so-called "Subjection of Women," they absurdly apply those terms to the condition of the wife in the modern society of the west—designations which are inappropriate even in the case of the inmate of Indian zenanas; and they speak of the modern worker as a "wage-slave," even though he is backed by a powerful trade-union. Passion has a language of its own, and poets and orators must doubtless be permitted to denote by the word "slavery" the position of subjects of a state who labor under civil disabilities or are excluded from the exercise of political power; but in sociological study things ought to have their right names, and those names should, as far as possible, be uniformly employed.
But this use of the word we may safely regard as a metaphor; nobody will assert that these laborers and women are really slaves. Whoever uses the term slavery in its ordinary sense attaches a fairly distinct idea to it. What is this idea? We can express it most generally thus: a slave is one who is not free. There are never slaves without there being freemen too; and nobody can be at the same time a slave and a freeman. We must, however, be careful to remember that, man being a "social animal," no man is literally free; all members of a community are restricted in their behavior toward each other by social rules and customs. But freemen at any rate are relatively free; so a slave must be one who does not share in the common amount of liberty, compatible with the social connection.
The condition of the slave as opposed to that of the freeman presents itself to us under the three following aspects:
First, every slave has his master to whom he is subjected. And this subjection is of a peculiar kind. Unlike the authority one freeman sometimes has over another, the master's power over his slave is unlimited, at least in principle; any restriction put upon the master's free exercise of his power is a mitigation of slavery, not belonging to its nature, just as in Roman law the proprietor may do with his property whatever he is not by special laws forbidden to do. The relation between master and slave is therefore properly expressed by the slave being called the master's "possession" or "property"—expressions we frequently meet with.
Secondly, slaves are in a lower condition as compared with freemen. The slave has no political rights; he does not choose his government, he does not attend the public councils. Socially he is despised.
In the third place, we always connect with slavery the idea of compulsory labor. The slave is compelled to work; the free laborer may leave off working if he likes, be it at the cost of starving. All compulsory labor, however, is not slave labor; the latter requires that peculiar kind of compulsion that is expressed by the word "possession" or "property" as has been said before.
Recapitulating, we may define a slave in the ordinary sense of the word as a man who is the property of another, politically and socially at a lower level than the mass of the people, and performing compulsory labor.
The great function of slavery can be no other than a division of labor. Division of labor is taken here in the widest sense, as including not only a qualitative division, by which one man does one kind of work and another a different kind, but also a quantitative one, by which one man's wants are provided for, not by his own work only, but by another's. A society without any division of labor would be one in which each man worked for his own wants, and nobody for another's; in any case but this there is a division of labor in this wider sense of the word. Now this division can be brought about by two means. "There are two ways" says Puchta "in which we can avail ourselves of the strength of other men which we are in need of. One is the way of free commerce, that does not interfere with the liberty of the person who serves us, the making of contracts by which we exchange the strength and skill of another, or their products, for other performances on our part: hire of services, purchase of manufactures, etc. The other way is the subjugation of such persons, which enables us to dispose of their strength in our behalf but at the same time injures the personality of the subjected. This subjection can be imagined as being restricted to certain purposes, for instance to the cultivation of the land, as with soil-tilling serfs, the result of which is that this subjection, for the very reason that it has a definite and limited aim, does not quite annul the liberty of the subjected. But the subjection can also be an unlimited one, as is the case when the subjected person, in the whole of his outward life, is treated as but a means to the purposes of the man of power, and so his personality is entirely absorbed. This is the institution of slavery."