The section sofa is a multi-piece sofa.  Common number of pieces are 3 and 5.  It can be arranged in a number of configurations.  The more pieces, the more configurations.  Ideally, any sectional you purchase will include fixtures that connect the pieces to keep them from separating.

Due to the massive and growing popularity of sectionals, there are many, many styles, designs and materials to choose  from.  Some are huge and can span large rooms while others are much smaller.

Two common configurations are L-shape and U-shape.