For most futures contracts, at any given time, one contract will typically traded much more actively than others. This is called variously the front month or the top step contract.
Financial contracts (such as bonds, short term interest rates, foreign exchange and stock indexes) tend to expire quarterly, in March, June, September and December.
This table lists the conventional letter codes used in tickers to specify delivery month:
January | F |
February | G |
March | H |
April | J |
May | K |
June | M |
July | N |
August | Q |
September | U |
October | V |
November | X |
December | Z |