These word are often used as interchangeable words, however, there is a big difference between them. Summary is about dispensing with unnecessary matters and presenting only what is needed. Summation, on the contrary, is about dealing with totaling all that is available. To put it differently, summary means briefing, while summation refers to totaling. Moreover, summary is used rather in an official sense, while summation occurs in mathematical context, while in legal sense, in the US, it means the conclusion of statements made by opposing counsel in a case. Summary in legal perspective means the right of a court to adjudicate immediately upon some matter arising during the proceeding.
