The term "master speed" in the Robert Frost poem of the same name refers to the enduring, timeless quality of love. The poet describes the transcendent quality of the bond between two people in love who are able to withstand the passing of time through memories.
Frost wrote the poem as a tribute to his daughter, Irma, and her fiancée, John Cone, on their wedding day in 1926. He first uses natural forms of speed, such as the movement of wind and water, to serve as a contrast to the speed afforded to two individuals who unite in love. This "master speed" is figurative, rather than literal, considering it cannot be measured or quantified. However, the ability for couples to form lasting memories that deepen the human bond transcends the physical aspect of life.
The final line of the poem, "Together wing to wing and oar to oar," is a metaphor for the unbreakable connection formed by two people who choose to join their lives together, a result of "the master speed." Interestingly, this line also appears on the gravestone Frost shares with his wife, Elinor, indicating the poem is autobiographical as well as a tribute to the eternal nature of love.