NT Transfer to Diamonds
The 2 response to 1N can be used as natural (rather than using Stayman or Jacoby), but it rarely is. This frees up the bid to use for any number of different conventions. In this case, it is used to show a weak hand with 5+ Clubs, and thus it asks partner to bid 3 which the 2 bidder intends to pass. As with all transfers, the purpose is to get the stronger hand to be declarer (so that the opponents cannot see the stronger hand in dummy).
When 2 is used as a transfer to Clubs, 2N is used as a transfer to Diamonds, which then requires a different way to invite notrump with a flat hand. This is done by bidding 2 (nominally, Stayman) over 1N and then rebidding 2N over any response by opener.
If you don't like the idea of bidding 2N that way, you can use 2 to transfer to 3, then you can pass with a Club suit or correct to 3 with Diamonds.