A "plurality vote" means that the person or option with the most votes wins. It's like a race where the winner is the one who gets the highest number of votes, even if they don't have more than half of the votes. Full definition
The spoiler effect is a problem in plurality voting systems because they enable a candidate to win with less than half of the vote. (en.wikipedia.org)
As user4012 has pointed out, the use of plurality voting in most election has led to a rigid two - party system. (politics.stackexchange.com)
Vote splitting most easily occurs in plurality voting because the ballots don't gather any information about the secondary preferences of the voters. (en.wikipedia.org)