What is Party Switching?

Legal Definition
Party-switching is any change in political party affiliation of a partisan public figure, usually one currently holding elected office.

In many countries, party-switching takes the form of politicians refusing to support their political parties in coalition governments. This happens particularly commonly in countries without firmly-established political parties, such as Vanuatu and French Polynesia where in 2004, a few members of various parties left the governing coalition, forcing it to collapse. Party switches often occur with the formation of new parties — witness the situation in the United Kingdom, where some Liberals moved to the Labour Party in the early twentieth century. In formerly communist countries in Europe, de-Sovietisation saw many Communist-Party representatives switch to other parties ranging on the political spectrum from socialist to conservative.

In some cases, the defectors from an opposition party may choose to support a ruling coalition. In Poland, for example, the exit of the populist Samoobrona party from the government prompted a number of its members to leave and form a new parliamentary group.

Party switching also occurs quite commonly in Italy, Ukraine, India, and the Philippines.
-- Wikipedia