First of all students must not confuse the accounts with ledgers. These are two totally different things. Even though these terms are loosely used for each other but they are certainly not the same. Ledgers can be regarded as big registers where we write up and update different accounts. So, it means accounts are specific places inside ledgers.
Coming back to the question, Nominal ledger is a ledger where impersonal accounts are maintained. As the suggests also, nominal means something related to numbers, that is why when we look at nominal ledger it has accounts like Capital, drawings, Purchases, Sales etc. Most of the personal accounts are maintained in Sales Ledger and Purchases Ledger.
Nominal ledger is also termed as General Ledger.
Please note, that this not a special kind of ledger or does not mean that it is a ledger that is kept outside of double-entry records. Nominal ledger is just another name given to General ledger and is NOT a ledger inside any ledger.