Public Television is a term used to describe a channel or station that is funded in some way by the governent rather than advertising, commercial sponsorship or subscription fees.
More often than not, a public television channel will have no advertising, except those for programmes or other channels.
Here in the UK, the BBC's two terrestrial television and many digital channels are funded by the television license fee. You are required by law to buy a license for your television, even if you "only use it for the VCR" (yeah, right). This license fee then pays for the programme production, broadcasting and technology research that the BBC undertakes.
It's mostly true that the BBC's programmes are of a higher quality than the commercial channels, but as technology has driven down the cost of programme making, other channels are now catching up.
Public Television also has a problem winning bids for high profile sports coverage; the money available simply isn't enough to pay the high fees demanded by the popular events. An example of this would be the Premier league football (soccer) coverage. British Sky Broadcasting (BSkyB) has a spending power far beyond that of the BBC, which unfortunately puts the coverage out of the reach of many football fans...
Although the BBC still does the best news coverage - commercial television still can't beat that :-)
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