Meaning of “simple” - Learner’s Dictionary

simple

adjective us uk /ˈsɪmpl/
His theories were simple, but profound.The book shows simple things you can do to reduce pollution from your car.The basic problem is very simple.The solution was simple but effective.The company has a simple formula for business success.
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)