What is "to ring in"

Ring \Ring\ (r[i^]ng), v. t. [imp. Rang (r[a^]ng) or Rung (r[u^]ng); p. p. Rung; p. pr. & vb. n. Ringing.] [AS. hringan; akin to Icel. hringja, Sw. ringa, Dan. ringe, OD. ringhen, ringkelen. [root]19.]

1. To cause to sound, especially by striking, as a metallic body; as, to ring a bell.

2. To make (a sound), as by ringing a bell; to sound.

   The shard-borne beetle, with his drowsy hums, Hath rung night's yawning peal.
   --Shak.

3. To repeat often, loudly, or earnestly.

   To ring a peal, to ring a set of changes on a chime of bells.

   To ring the changes upon. See under Change.

   To ring in or To ring out, to usher, attend on, or celebrate, by the ringing of bells; as, to ring out the old year and ring in the new.
   --Tennyson.

   To ring the bells backward, to sound the chimes, reversing the common order; -- formerly done as a signal of alarm or danger.
   --Sir W. Scott.