"party affiliation" refers to the political group or party that a person is associated with or supports. It shows which party's ideas, beliefs, and values the person agrees with and wants to promote. Full definition
Under the state's system, the two candidates who receive the most votes regardless of party affiliation move on to the general election. (politicalticker.blogs.cnn.com)
People can now go online to sign up to vote, change their address for voting purposes, and switch party affiliation. (wamc.org)
Of course, as that link states, there's not much stopping me from changing party affiliation at any time and voting in whatever primary I choose. (politics.stackexchange.com)