40-day long Lent is considered to be the most important out of the four long fasts. After the Lent comes the Fast Week in remembrance of the last days of Jesus Christ's life on the earth and his torments.
The Lent means for Orthodox believers not only a refusal from definite food, but as well a refusal from bad habits and entertainment. It's the time of meditation and zealous prayers. The aim of any fast is exercise in continence, purgation of soul from temptations and sin thoughts, and subdue of soul and body to Holy Spirit.
In the old times in Russia seriously ill people, pregnant women, feeding mothers, warriors, people involved in hard physical labor and people in the road were freed from the Lent. However, they strictly kept a spiritual Fast, abstaining from entertainment and repented of violating the Lent at confessions.
The Orthodox Church calls for abstaining from eating and drinking meat, milk, eggs and fish, including in various dishes, in the course of the Lent.