During the winter months the grass dies out and goes dormant until spring.
The reason the grass dies out in the winter is because the soil gets too cold and there's usually not enough sunlight out in the winter months for the grass to grow.
It's basically due to the frost and cold temperatures where the grass is unable to grow and thrive so it dies out or goes dormant and then when the weather and soil warms up and rain gets to the grass more often the grass begins to grow once again.
It's very normal for grass to die out during the fall and winter and then come back during the spring and warmer months.
Trees most commonly do the same thing as well as they go dormant during the winter and then in the spring they return.