The joining of two or more pieces of fabric by sewing through both pieces.
There are a number of ways to construct and finish seams.
These pattern pieces will be sewn together along the Centre Back line (green dashed line), creating a seam.
The shaded pink area will be the seam in the fabric when they are sewn together.
When the fabric is cut and the two pieces are sewn together, the seam can be seen on the inside. In this case the seam is pressed open.
In this image, the seam has been pressed to one side rather than pressed open.