The Saturday morning cartoon was a term coined in the 1960s which was the name for animated television programming done on every Saturday morning by every major television networks (ABC, CBS, FOX and NBC) starting in the 1960s until the early 1990s. Saturday morning cartoons were often referred to as a form of animation known as illustrated radio. It was known as this due to its stress not on its visual prowess but instead on the voice acting and sound effects. These cartoons were often known as animations for children due to the fact that children are more interested in gags and what is presented, but not the quality of the presentation.
The usual time slot for these cartoons, on the major networks, is between the hours of 8am until noon. It is important to note that until 1980 the major networks would often have Sunday morning cartoons as well. The difference between the Saturday and Sunday morning cartoons lay in the fact that on Sunday the networks would often recycle old Saturday morning cartoons which had been canceled in the past. 
In 1996 ABC was bought by The Walt Disney Company. At this time the block of Saturday morning cartoons on the channel was now known as Disney's One Saturday Morning. In 2001, ABC started to air solely Disney produced programs; also at this time the block began airing a mixture of live-action and animated shows.
In 1999 CBS got brought out by the large company Viacom (owners of other networks such as MTV, VH1 and Nickelodeon).  Directly after its merger CBS began airing solely Nickelodeon based programs on Saturday mornings. Many of these shows were for very young children with shows such as Blue's Clues being part of the programming block. In mid 2006 the merger ended and CBS began airing a new block of cartoons.
Starting in 1990 FOX tried an interesting approach to cartoons, instead of using Saturday mornings, they would often air children based cartoons starting at 3pm on weekdays, as to target the childhood audience right after school let out. However, starting around 2002 FOX abandoned this idea and started to air programs on Saturday mornings known as 4Kids TV. This programming is now four hours long every Saturday morning on FOX. 
After dropping their Saturday morning cartoon series, NBC began a partnership with the Discovery channel and started programming known as Discovery Kids. They started airing original shows at the beginning of 2006.