Haphazard sampling is a sampling method that does not follow any systematic way of selecting participants. An example of Haphazard Sampling would be standing on a busy corner during rush hour and interviewing people who pass by.
Haphazard sampling gives little guarantee that your sample will be representative of the entire population. If you were to use this method to conduct a survey to find out who people will vote for president, the results you get may not predict the actual outcome of the election. This is because you would probably only be able to interview people who were probably white-collar workers on their way to work, or those who were not in such a big hurry to get to where they're going, or those who lived or worked near the area where you conducted your survey.