It's a shortened form of Explain
like I'm five years old.
I'm not sure whether this already has the status of an idiom, but it's quite frequently used.
The meaning is quite literal:
Explain a complicated subject in a way a five year old can understand.
ell.stackexchange.com/users/12661/Stephie
The phrase means 'explain it to me in very simple terms, as if I were only five years old'.
Whilst someone using this might mean that they really don't understand, it is also possible that the person asking suspects that the person explaining doesn't really understand either and is only parroting jargon.
ell.stackexchange.com/users/29023/No'am Newman
It means, "Please explain it to me in the simplest possible terms, as one might explain it to a five-year-old child.
" I sometimes say that to someone who is explaining technical matters of computing to me, for instance, where I am reasonably computer-literate but know little or nothing about programming or the inner workings of my laptop.
Does this make sense?
It's not an insult, it's just a request for a patient, easy to understand explanation.
ell.stackexchange.com/users/26939/Mark Hubbard
To fully answer this question, one must first examine the underlying assumptions of the statement
"Explain like I'm five", mainly, what does it mean to "Explain" and what is the relevance of being "five".
Let us first elucidate the bourn of this directive.
For the sake of clarity, we should begin by prescribing to the aesthetic justification of Occam’s razor.
As Thomas Aquinas stated, "If a thing can be done adequately by means of one, it is superfluous to do it by means of several; for we observe that nature does not employ two instruments [if] one suffices.
" With this in mind, it is most likely that an unobfuscated exegesis is being solicited from the requester.
In Stephen R. Shirk’s book, “Cognitive Development and Child Psychotherapy”, he states that “By recognizing the implications of the self-definition in a social and psychological context, the 15-year-old’s response can be said to be developmentally advanced relative to that of the 5-year-old.”
One can only assume that the intersection of the definitional self and the subjective self is the key factor in having chosen “five” as the conditional context for the desired exposition.
ell.stackexchange.com/users/29115/The B
"Explain like i'm five" simply means that the explanation should be elaborate at the same time very easy to understand.
The situation should be explained in its most elementary form, as one would explain something to a five year old child.
The explanation should be detailed and should be elaborate enough, yet explained in its simplest form.
ell.stackexchange.com/users/27122/Varun Nair
This phrase is used primarily in the academic and professional world, and typically in one of three scenarios.
In one situation, the person requesting the explanation does not fully understand the concept or situation being discussed, and is requesting a basic explanation that uses simpler terms.
The explanation will probably include a number of oversimplified analogies.
In this scenario the person asking might not have a personal relation at all to the subject matter; however, academics and professionals from nearly related fields may use this phrase to indicate some interest in their colleagues' work.
Here, it would mean something like, "I'm not sure I understand, but I am interested - please explain this idea to me."
In another situation, two persons may be having a professional discussion in which a superior is asking a subordinate (or potential candidate) for a brief demonstration of real understanding.
This typically takes the form of a question posed during a job interview, but is also occasionally used during other certification interviews.
In this context, it means something more like "Please demonstrate for me that you understand the most essential elements of the subject."
The final scenario is also typically between two working professionals, but is spoken more abruptly, in a manner that indicates frustration or impatience.
In this situation the meaning becomes "I am very busy, but I need to fully understand what you're trying to explain.
Slow down, and give me the most important parts.
" This usage would typically follow some kind of inter-disciplinary interaction concerning a growing problem.
One might imagine an accountant explaining his changing needs to a software engineer.
ell.stackexchange.com/users/29111/Sean Boddy
Let me explain this to you, like you were only five years old... ...
it means, making a complicated matter easy to understand.
Like you would do for a little child with limited understanding.
ell.stackexchange.com/users/29131/Levite
In my recent  question , I got this  link  in an answer.   Here, ' Explain like I'm five ' is written. I tried to find its meaning on the Internet, but I got only an acronym ELI5.   Is 'explain like I'm five' a phrase or an idiom? What does it mean?
What is 'explain like I'm five'?
ell.stackexchange.com
<meaning><meaning-in-context>
ell.stackexchange.com/questions/79280
ell.stackexchange.com/users/12300/Rucheer M
 It means, "Please explain it to me in the simplest possible terms, as one might explain it to a five-year-old child. The phrase means to explain something in simple terms, as if to a small child.
The phrase means to explain something in simple terms, as if to a small child.