All that you say before the tax officer, documents that you show him, and all that he records in his minutes are called as evidence. These pieces of evidence corroborate your income and convince the tax department that you submitted your correct income in your tax return. And evidence that appellate allows you to show before them for the first time is called additional evidence. Let me elucidate it in the ripple below.
What is evidence?
If you have attended any scrutiny case, then you may recollect that
In tax jargon, these minutes and submissions are called evidence.
What is additional evidence?
If you are unsatisfied with AO's (tax officers) order then you can file an appeal before appellate bodies.
You can present your case before the appellate. In this presentation you can submit only those documents that you submitted before the AO.
Tax law generally doesn't allow you to submit any evident that you didn't submit before the assessment officer.
Law is not that air-tight too. In case, there is need you can plead before the Appealed officer to show some more documents.
If the officer agrees then he can let you produce those documents. These additional documents are called additional evidence.
Now in brief:
Additional evidence is the evidence that