In Classical Tonal music, there are various types of cadence, i.e. the chords that close a musical phrase.

They are::

• The Perfect Authentic Cadence (PAC). Special form of V - I
• The Imperfect Authentic Cadence (IAC). Some form of V - I.
• The Half Cadence. Some form of 'x' - V, wher 'x' is any chord that goes to V. Also know as an Open Cadence.
• Plagal Cadence. Some form of IV - I. If iv - I, or iv - i, then it's a Minor Plagal Cadence
• Plagal Half-Cadence. Some form I - IV.
• Interrupted (or Deceptive) Cadence. V - vi, or V - VI (in minor key).

Click here for an audio-visual example of these types of cadence.

• A device often used to delay an Authentic Cadence (V - I) is the Cadential 64. Here's how it works:
  
  
  
  Simetimes the Cadential 64 is written as I64 (instead of V64). Both are slightly incorrect descriptions of the same thing, using different aspects of the normal conventions of Roman Numeral Analysis.
  
  I64 is a I chord in 2nd inversion, but it functions as a V chord with 2 suspensions.
  
  V64 is not a V chord in 2nd inversion, but it does function as a V chord with 2 suspensions.
  
  More information about the Cadential 64 is here.