First of all, “conference interpreting” is used more often: about 239,000 occurrences of the term. “Conference interpretation” only gives about 69,700 results in Google.
Definition: both terms essentially refer to the same thing – conference interpreting or interpretation is a specialization of language interpreters. Conference interpreting is in most cases simultaneous, and professional interpreters support various types of events such as conferences, meeting, congresses etc.
Conference interpreting is distinctly different from other types of interpretation, for example, court, medical or community.There is specialized degrees, for example, Master of Arts in Conference Interpretation (MACI).
What about the difference then about “interpreting” and “interpretation?”
“Conference interpretation” is a product that a simultaneous or conference interpreter produces: “His conference interpretation was flawless.”
While this may not be a very important difference, sometimes it is semantically important. Most books about the profession, for example, have “simultaneous interpreting” in their titles.