The Rover has several layers of significance. First, it is a tribute to King Charles II. After his father's execution and during the interregnum, a period of strict Puritan rule in the country, Charles roved around Europe, having a good time.
Second, the title refers to the character of Willmore, a navy captain who roves or wanders the world as a cavalier. He not only travels around widely but has a roving, bawdy eye. He likes to pursue women sexually, moving from one to the next.
Finally, the title also refers to Hellena. Destined for the convent by her family, Hellena roves away from that plan and takes her destiny into her own hands. She wants love, not a nunnery, and she goes after it. She is willing to take risks and behave unconventionally. For example, at one point she disguises herself as gypsy so she can go to the carnival, a subversive act.
The Rover is a celebration of the Restoration, not only of the monarchy but of the theater, which had been shut down as immoral. Behn makes the most of the new liberalism to explore sexual dynamics and portray a woman who is willing to challenge the constraints placed on her.