Something which is very easy to do
Origina piece of cake
It is thought that this idiom originated in the 1870s when it was tradition to give cakes as prizes in competitions. In some parts of the USA at this time, slaves would participate in ‘cake walks’ where couples would perform a dance mocking the mannerisms of their masters. The most graceful couple would receive a cake as a prize. From this, the expression ‘a piece of cake’ started being used to describe something that was easy to achieve.