A latent defaulter is someone who visits a website because their default homepage is pre-set to that address, or are redirected to a particular website, through no action of their own. They do not purposely choose to visit the website but their visit is counted towards a website's traffic statistics, even though they may immediately leave the website.
When someone buys a new computer the installed browser has the homepage pre-set by default. When they open a browser window they automatically visit the website that has been pre-set. Alternatively when someone logs out of an email service, or instant messenger client, they can be automatically redirected to a particular website. These people are "latent defaulters".