Remote linking is pulling content (images or scripts) from a different web site rather than using copies hosted on the same site. This is a bad practice because it means that the image or script is disabled whenever either of two sites is unavailable instead of only one site making it twice as likely to have problems. Also it makes the page slower to load.
Finally where you have free hosting remote linking from that hosting will not be permitted as it will be using bandwidth without any payment for bandwidth used (free sites usually display ads which earn the money to pay for the bandwidth).
