In the common usage of this word it refers to something done by one person or a group for another. Service may be sold or be rendered out of love and gratitude. Professionals like architects, dentists, tailors and so on sell their services. I would call it a service out of love when a mother nurses her child. An obedient son making sure that his parents are comfortable and in peace is also, in my view, a service that the son does out of love for his parents. In the Eastern philosophy there is a mention of service to the master that a disciple does out of his love for the master. I’d call someone performing the service of second kind as virtuous whereas someone performing the first would be called a skilled person. The kind of wealth earned by performing each type of service is also different.
There are some subtle differences in the way the practitioners of these two kinds of services usually perform them.
An architect for instance makes sure that the design of the home that he does makes the client happy. Architect’s own personal preferences about a home take the back seat. A tailor’s personal preferences about dressing takes a back seat when he stitches the client’s clothes — the client has to feel happy and satisfied about the dress. Client first is their mantra.
It is not exactly the same when one performs the "out of love" type of service — the idea of putting the happiness of the served one before one’s own desires is often lost. Often the serving won’t even be aware that his own desires to prove something or to fulfil some selfish motive out of it are coming in the way.