Poetry uses forms and conventions to suggest differential interpretation to words, or to evoke emotive responses. Devices such as assonance, alliteration, onomatopoeia and rhythm are sometimes used to achieve musical or incantatory effects.
The average speed of an object tells you the (average) rate at which it covers distance. If a car's average speed is 65 miles per hour, this means that the car's position will change (on the average) by 65 miles each hour.
An example of a speed is '45 miles per hour.' An example of velocity is '45 miles per hour west.' In the real world, people often ignore the importance of including direction in a velocity measurement, so the words speed and velocity sometimes become interchangeable.