As the name implies, it is a Non-Accounting voucher whose entries do not affect your accounts at all. The entries in this voucher are not posted into ledgers, instead are stored in a separate Memo Register. A Memo Voucher can be converted into a regular voucher, to be included in your books of accounts.
Gateway of Tally.ERP à Accounting Voucher à Click on F10 :
This type of Memo Voucher, which can be used in many situations such as..
Suspense Accounts : Suppose an employee takes an advance for his traveling expenses. Until and unless the expenses are incurred, the actual expenditure details cannot be worked out. A Memo Voucher can be entered for advance and can be turned to a Payment Voucher after receiving the details of the expenditure incurred.