Meaning of “simple” - Learner’s Dictionary

simple

adjective uk us /ˈsɪmpl/
EASY

A2 not difficult to do or to understand:

[ + to do sth ] It's very simple to use.
Just mix all the ingredients together - it's as simple as that.
NOT COMPLICATED

B1 not complicated or containing details that are not necessary:

a simple life
a simple black dress (= dress without decoration)
IMPORTANT

B2 used to describe the one important fact, truth, etc:

We chose her for the simple reason that she's the best person for the job.

(Definition of “simple” from the Cambridge Learner’s Dictionary © Cambridge University Press)