Line - The scanning of a TV picture is performed in a series of horizontal lines. In an interlaced scan, a frame consisting of the odd-numbered lines is followed by a frame consisting of the even-numbered lines. The 2 frames together make up a complete picture. The number of lines is a convenient measure of the resolution of a TV picture; the larger the number of lines the greater the resolution. Standard analog TV formats have 525 (NTSC) or 625 (PAL, SECAM) lines in total. HDTV systems may have 1000+ lines.
  
Although the total number of lines is usually quoted, often a better measure of resolution is the number of visible lines.