Third parties in the united states typically represent women's interests. extremist religious groups. recent immigrants. the political interests of america's allies who attempt to influence the american decision-making process because u. s. policies can affect their futures. social and economic interests that are disregarded by the two major parties for certain reasons.

The answer is: social and economic interests that are disregarded by the two major parties for  certain reasons.
Two major political parties in united states (democratic party and the republican party) represent the interest for the majority of the people in united states, and those interest tend to contradicts one another.
The existence of third party usually indicates that there are some percentage of citizens that want something that lies in the middle of these two major political parties.

It all depends on the individual