The title of Jonson's poem – "Slow, Slow, Fresh Fount" – isn't really the title. Well, it is and it isn't. After all, the poem is part of a play Jonson wrote called Cynthia's Revels, so there's that title to contend with, too. And some critics refer to these lines as "Echo's Song" (because the nymph is singing them in the play), which gives us yet another title to consider.
In this case, though, we'll go ahead and call this one by its most common name, "Slow, Slow, Fresh Fount," and we're doing so with good reason. Often when poems are taken from plays, they are simply titled after the first line of the poem. In this case, the first line is Echo's address to the "gentle springs" (2). She wants those springs to sing along with her, to "keep time" with her song of mourning.
And what are those springs? Good question. The "fount" refers to what Echo, earlier in the play, calls the "mourning fount," a spring or body of water where (she suggests) Narcissus fell in love with his own reflection and died. She's calling to the place of her loved one's death and asking that place to mourn along with her.