Bank Holidays

Public Holidays in Britain are generally called "Bank Holidays" as the Bank of England closed on these days. In England and Wales there are 8.
Four relate to the two christian festivals of Christmas and Easter. Christmas Day, (celebrating the birth of Jesus Christ) on the 25th December is a holiday as is the 26th of December called "Boxing Day" as it was traditionally the day that servants got a holiday and present from their employer. If Christmas or Boxing Day fall on a Saturday or Sunday the Monday/ (and Tuesday) after are holidays.
 The Friday before Easter Sunday is a holiday. It is called "Good Friday" as it is supposed to be the day that Jesus Christ was crucified. The Monday after Easter Sunday, is also a holiday called Easter Monday. 
Easter is not a fixed holiday and different christians had different ways of calculating it but all Roman Catholic and Protestant churches now calculate it as the first Sunday after the first full moon after the spring equinox, so it can vary from late March to mid-April. 
Otherwise Bank Holidays are generally not on a particular date but a particular Monday so that there is a long weekend.
The complete list of holidays is
!st January
Good Friday
Easter Monday
The first monday in May (Mayday)
The last Monday in May  (Spring Bank Holiday)
The last Monday in August (Summer Bank Holiday)
25th December (Christmas Day)
26th December  (Boxong Day)

Except for Xmas day when everything shuts down , like the morning of Eid el Ahda, schools and factories are shut but shops and tourist attractions are open. For the spring and summer holidays particular events such as music festivals and  country shows are organised for those days to attract visitors from the cities to spend money. As everyone want Bank Holidays to be sunny to enjoy these events or go to the seaside, and as it rains a lot in Britain the joke is always that if it is a Bank Holiday it will rain.

Workers must get 20 days paid holidays a year and the 8 Bank Holiday days can count towards them although most people get them as well. Depending on the employer you may be able to  choose when to take your 20days or the whole factory may shut down at a particular time. Lots of firms close for the 3 days between Christmas and New Year. (All schools and most offices and factories have Saturday and Sunday off work each week).