I had a little "tour" around the net, being myself a little confused about this point, too.
I found so many explanations, that one gets even more confused after reading them...
Here is what Wikipedia says:
"Oral and written language
An individual language user's deviations from standard language norms in grammar, syntax, pronunciation and punctuation are sometimes referred to as errors
However in light of the role of language usage in everyday social class distinctions, many feel that linguistics should be descriptive rather than prescriptive to avoid reinforcing dominant class value judgments about what linguistic forms should and should not be used. One may distinguish various kinds of linguistic errors – some, such as aphasia or speech disorders, where the user is unable to say what they intend to, are generally considered errors, while cases where natural, intended speech is non-standard (as in dialects), are considered correct speech in descriptive linguistics, but errors in prescriptive linguistics."
I also visited some forums, and English learning sites; look at the difference of opinion, it is absolutely amazing:
1) "The first point I would like to make is that if we know the students then we are able to detect 'slip-ups' compared to actual mistakes. To my mind mistakes and errors amount to the same thing when we are marking but not grammatically, of course
. I made a mistake and I erred are so similar as to be inseparable.I, personally, give the student the opportunity to correct the mistake him/herself, possibly guiding thought depending on the mistake, and if he/she is unable to do so then, and only then, do I correct the mistake. Underlining is the initial indicator that they have made a mistake and, more often than not, the student will realise what the mistake is.We should give them the opportunity to correct their mistakes and realise why they have erred!"
2) "I think an error is something you make unknowingly such as missing out a letter while reciting the alphabet. A mistake is something you make knowingly but turns out to be wrong such as revising a chapter that doesn't come up in an exam."
3) "The two words mean the same thing but there are times when only one will do. For example in this sentence only mistake would be appropriate: 'It was a mistake to ask Helen to come on the trip'. Alternatively 'This was a serious error of judgement.' Mistake cannot be used in this sentence. Sometimes it's not so obvious. 'I looked at his maths homework and there were number of errors in is calculations.' In this sentence error is better. 'You have made a number of mistakes in your English essay'. Here mistake is more appropriate."
And it goes on... the list is endless!
So, I asked our friend, the dictionary and here is what it says:
(Oxford Advanced Learner's Dictionary):ERROR:a mistake
, especially one that causes problems or affects the result of somethingNo payments were made last week because of a computer error.error in something There are too many errors in your work.error in doing something I think you have made an error in calculating the total.A simple error of judgement
meant that there was not enough food to go around.a grave error
(= a very serious mistake)a glaring error
(= a mistake that is very obvious)
The delay was due to human error
(= a mistake made by a person rather than by a machine).The computer system was switched off in error(= by mistake).
There is no room for error in this job.
Almost all accidents start with a simple error by the pilot.MISTAKE
1) an action or an opinion that is not correct, or that produces a result that you did not wantIt's easy to make a mistake
.This letter is addressed to someone else—there must be some mistake
.It would be a mistake to ignore his opinion.Don't worry, we all make mistakes.You must try to learn from your mistakes.Leaving school so young was the biggest mistake of my life.
I made the mistake of giving him my address.
It was a big mistake on my part to have trusted her.
a great/serious/terrible mistake
It's a common mistake(= one that a lot of people make).
2 a word, figure, etc. that is not said or written down correctlySYNONYM
errorIt's a common mistake among learners of English.
The waiter made a mistake (in) adding up the bill.
Her essay is full of spelling mistakes.
I've got even more confused. What about you?