The term exchange rate ( used in English also alternate picking ) refers to a technique for stringed instruments, especially for guitars.
Guitar playing technique on acoustic ( concert )
For use come right index and middle fingers ( in notation and tablature usually with I and M for short). In exchange now beat the index and middle fingers of the right hand on a string or alternating different strings. In practice, often starts the index finger, followed by the middle finger. Depending on the further order of the melody but it can also be technically inconvenient to do so. Then the middle finger should begin. If not the lowest - ie usually 6 - string ( "E") is activated, it is possible to apply the different-sounding alternate picking techniques Apoyando or Tirando.
Technique in electric (jazz ) guitar / electric guitar
Here one uses a plectrum. This is moved to and deductions possible small deflection by moving the wrist on the string.