A political party faction is a relatively organised group within a political party which competes for power and influence within the party. It exists because:-
Factions are not necessarily a bad thing, as they may help to keep the party together by letting different groups feel that they can have some impact and allowing a range of ideas to be aired.
However, if intense conflict develops between different factions it can weaken the party, for example that between left and right in the Labour Party in the early 1980s, which led to a breakaway group forming a new party, the Social Democrat Party.
Other examples are the tensions between pro and anti EU factions in the Conservative Party during the Major premiership and that between Blairite and Brownite factions within Labour at the end of the Blair premiership and into the Brown premiership. This has changed in recent years to Corbynistas – those who support Jeremy Corbyn – within the Labour Party.