Interlace

The PAL television standard uses 625 horizontal lines to create a single frame of picture. Odd numbered horizontal lines are recorded as one image followed 1/50 sec (or 1/60 sec for NTSC) later by the even numbered lines as a second image. Each separate image is called a field and two fields are combined to form a frame. The picture is made by displaying 50 interlaced fields per second and is known as 'interlaced scan' or 'interlaced'.