The phrase "internal poll" refers to a survey or study that is conducted within a particular group or organization. It is not meant for the general public, but rather to gather information from members within that specific entity. Full definition
At the least that independent poll gives the lie to internal polls from each camp that had its candidate five points up. (hudsonvalleyone.com)
Her campaign has tried to paint a different picture, saying that the race is closer than public polls suggest; the campaign's own internal polls say it's all tied up. (washingtonpost.com)