Just for final clarification, if anyone is still unsure:
Lent is the period between Ash Wednesday and Easter Sunday (this year on 9th February and 27th March respectively), and is 46 days long, as stated by sillyyank. It is, as said, to represent the 40 days Jesus spent in the desert, and is set in the run-up to Easter to help calm and prepare for the Easter celebration. The reason for the difference in nuber of days between the actual length (46 days) and the symbolic length (40 days) is because Lent was devised during a historical period when Sundays were feast days. Thus, because Sundays would have been the one day everyone ate well, Lent was "suspended" on the six Sundays during Lent, so to make sure that the actual period of abstinence wasn't lost an extra 6 days were added to the period.
This means, then, that on all of the Sundays between Ash Wednesday and Easter Sunday you may consume/do what you have given up, just for the day, and it doesn't matter, because those days don't count.
I hope that clears it all up.