A digital wallet is simply tokenization of money, digitally! Apps and Banking Systems can use it very differently. In the Banking system this can (for example) be treated as a Nostro or Escrow holding, or a sub-titled account. The wallet can contain a previously defined payment instrument (think credit card credentials) or a digital equivalent of the base currency (think US Dollars), stored and kept digitally.
A mobile wallet, is simply the digital wallet on the mobile handset (and in some cases the carrier).
A mobile wallet, is simply the digital wallet on the mobile handset (and in some cases the carrier).