The document introduces semantic segmentation, a deep learning task that classifies each pixel in an image into different classes, contrasting it with instance segmentation. It highlights the importance of pixel-level understanding for applications like self-driving cars and robotic systems, and discusses the Fully Convolutional Network (FCN) model architecture used for this task. The FCN processes images through down sampling and up sampling to maintain semantic and spatial information, utilizing skip connections to aid in feature merging.