Yom Tov is a the Hebrew term for a Jewish Festival. Quite simply, "Yom" means "Day" and "Tov" means "Good" - so it literally means "Good Day".
The following days would usually count as Yamim Tovim (the plural - in Hebrew, the adjective - "Tov" - must agree with the noun - "Yom" - so when "Yom" is pluralised to "Yamim", "Tov" is pluralised to "Tovim").
All these days have similar restrictions against work to Shabbat, although with the exception of Yom Kippur (the holiest day in the Jewish year), are less important than Shabbat. Orthodox Jews will take off these days as holiday (usually out of their annual leave allocation) and go to Synagogue. (Although Pesach and Succot have "intermediate days" - "Chol HaMoed" - in the middle, on which one can work if necessary.)
There are also two well known Jewish festivals which don't have the status of "Yom Tov".
While these are important, there are no restrictions against work on these days and they are significantly less important than the Yamim Tovim mentioned above.
See also Second day Yom Tov for some information on the length of the festivals.