Hello dear friend! :)
Well, fasting in general is primarily the act of willingly abstaining from some specific foods. Lent is one of the many fasting periods, the period of 40 days which comes before Easter in the Orthodox Christian calendar. It is observed by many Christian denominations (with differences). As far as Orthodox Christianity, Great Lent is the longest and strictest fasting season of the year that for 40 days in a row we abstain from meat, meat products, fish, eggs, dairy, wine and oil.
In Orthodoxy there are three types of fasting: the Ascetic, the Eucharistic and the Total fast. Orthodox Christians apart from the main periods of extended fasting, they are fasting in a weekly basis (Wednesdays and Fridays). The purpose of fasting is to guard against gluttony and impure thoughts, deeds and words.
I know that these are propably too many information, so I have to stop here, even there are more to say :)
God bless you!