Television is a self-reflexive technology that builds off of itself. By this I mean programming on television talks about other things on TV. For example, this often occurs on a comedy sitcom where a person will joke about how their station is better than a rival broadcasting station. A more common instance where TV speaks about itself is shows that literally just review what happened on other shows, generally reality shows and news programs. Programs like Entertainment Tonight and The Colbert Report are examples of recaps of what has happened recently on TV.
In a sitcom, self-reflection of TV can be seen in the Procenium arch, where an implied TV is. The Procenium arch is essentially the wall that is open to us to see the show, from the well-known basic living room set up of TV sitcoms. This is often a focus on shows where a character looks to this implied TV.
Two examples of this in shows are That 70's Show and Family Guy. In That 70's Show you can see a scenario where the classic living room is viewed, with the 'missing wall' being the angle from which we view the scene. The TV is smashed by the bowling ball and becomes the conflict of this episode.
In Family Guy, often times the characters offer their take or input on a show in a sarcastic and humorous way as seen in this scene;
Even though I completely disagree with Family Guy hating on the best show known to man, The Office, this clip shows yet again how a sitcom can involve other programming into its own.
Now here are a few more clips that relate to other shows;
And here are a few more where characters from other shows have appearances;